Method for producing pressure-responsive particles, method for producing printed material, method for producing sheet for producing printed material, and pressure-responsive particles

ABSTRACT

A method for producing pressure-responsive particles includes: adding an aggregating agent to a dispersion containing composite resin particles containing a styrene-based resin including a styrene compound and a vinyl monomer other than the styrene compound as polymer components and a (meth)acrylic acid ester-based resin including a (meth)acrylic acid ester compound as a polymer component to aggregate the composite resin particles so as to form aggregated particles A; forming a shell by adding an aggregating agent and styrene-based resin particles containing a styrene compound and a vinyl monomer other than the styrene compound as polymer components to a dispersion containing the aggregated particles A to aggregate the styrene-based resin particles so as to form aggregated particles B; and heating and fusing the aggregated particles B to form pressure-responsive particles. The amount of the styrene-based resin particles added in the formation of the shell is 5 mass % or more and 40 mass % or less relative to the total mass of the composite resin particles. The amount of the aggregating agent added in the formation of the shell is 0.1 mass % or more and 1.0 mass % or less relative to the total mass of the composite resin particles. The mass ratio of the styrene-based resin to the (meth)acrylic acid ester-based resin in the pressure-responsive particles is from 80:20 to 20:80. A difference between the lowest glass transition temperature and the highest glass transition temperature of resins contained in the pressure-responsive particles is 30° C. or more.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 fromJapanese Patent Application No. 2021-054291 filed Mar. 26, 2021.

BACKGROUND (i) Technical Field

The present disclosure relates to a method for producingpressure-responsive particles, a method for producing a printedmaterial, a method for producing a sheet for producing a printedmaterial, and pressure-responsive particles.

(ii) Related Art

Japanese Unexamined Patent Application Publication No. 2018-053220discloses a releasable sheet that allows opposing surfaces thereof to bereleasably bonded to each other. The releasable sheet includes asubstrate sheet, a pressure-sensitive adhesive layer on at least onesurface of the substrate sheet, and a surface layer on a surface of thepressure-sensitive adhesive layer. The pressure-sensitive adhesive layercontains an adhesive base containing a natural rubber-based material.The surface layer contains at least one selected from the groupconsisting of cellulose nanofibers, chitin nanofibers, and chitosannanofibers.

Japanese Unexamined Patent Application Publication No. 2021-017465discloses an adhesive material containing a styrene-based resincontaining styrene and a vinyl monomer other than styrene as polymercomponents and a (meth)acrylic acid ester-based resin containing atleast two (meth)acrylic acid esters as polymer components. The masspercentage of the (meth)acrylic acid esters relative to the total massof the polymer components of the (meth)acrylic acid ester-based resin is90 mass % or more. The mass ratio of the styrene-based resin to the(meth)acrylic acid ester-based resin is from 80:20 to 20:80. Theadhesive material contains resin particles having at least two glasstransition temperatures. The lowest glass transition temperature is −30°C. or lower, and the highest glass transition temperature is 30° C. orhigher.

SUMMARY

Aspects of non-limiting embodiments of the present disclosure relate toa method for producing pressure-responsive particles including: anaggregating step of adding an aggregating agent to a dispersioncontaining composite resin particles containing a styrene-based resinincluding a styrene compound and a vinyl monomer other than the styrenecompound as polymer components and a (meth)acrylic acid ester-basedresin including a (meth)acrylic acid ester compound as a polymercomponent to cause aggregation so as to form aggregated particles A; ashell forming step of adding an aggregating agent and styrene-basedresin particles containing a styrene compound and a vinyl monomer otherthan the styrene compound to a dispersion containing the aggregatedparticles A to cause aggregation so as to form aggregated particles B;and a fusing step of heating and fusing the aggregated particles B toform pressure-responsive particles. This method producespressure-responsive particles that may have better tackiness at the timeof pressure bonding and provide higher dispersion storage stability andthat may generate less aggregates and fusion-bonded materials than amethod in which the amount of the aggregating agent added in the shellforming step is less than 0.1 mass % or more than 1.0 mass % relative tothe total mass of the composite resin particles or the mass ratio of thestyrene-based resin to the (meth)acrylic acid ester-based resin in thepressure-responsive particles is from more than 80:less than 20 to 100:0or from 0:100 to less than 20:more than 80.

Aspects of certain non-limiting embodiments of the present disclosureaddress the above advantages and/or other advantages not describedabove. However, aspects of the non-limiting embodiments are not requiredto address the advantages described above, and aspects of thenon-limiting embodiments of the present disclosure may not addressadvantages described above.

According to an aspect of the present disclosure, there is provided amethod for producing pressure-responsive particles including: adding anaggregating agent to a dispersion containing composite resin particlescontaining a styrene-based resin including a styrene compound and avinyl monomer other than the styrene compound as polymer components anda (meth)acrylic acid ester-based resin including a (meth)acrylic acidester compound as a polymer component to aggregate the composite resinparticles so as to form aggregated particles A; forming a shell byadding an aggregating agent and styrene-based resin particles containinga styrene compound and a vinyl monomer other than the styrene compoundas polymer components to a dispersion containing the aggregatedparticles A to aggregate the styrene-based resin particles so as to formaggregated particles B; and heating and fusing the aggregated particlesB to form pressure-responsive particles, wherein an amount of thestyrene-based resin particles added in the formation of the shell is 5mass % or more and 40 mass % or less relative to a total mass of thecomposite resin particles, an amount of the aggregating agent added inthe formation of the shell is 0.1 mass % or more and 1.0 mass % or lessrelative to the total mass of the composite resin particles, a massratio of the styrene-based resin to the (meth)acrylic acid ester-basedresin in the pressure-responsive particles is from 80:20 to 20:80, and adifference between the lowest glass transition temperature and thehighest glass transition temperature of resins contained in thepressure-responsive particles is 30° C. or more.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present disclosure will be described indetail based on the following figures, wherein:

FIG. 1 is a schematic view of one example of a printed materialproducing apparatus according to an exemplary embodiment;

FIG. 2 is a schematic view of another example of the printed materialproducing apparatus according to an exemplary embodiment; and

FIG. 3 is a schematic view of the other example of the printed materialproducing apparatus according to an exemplary embodiment.

DETAILED DESCRIPTION

Exemplary embodiments of the present disclosure will be described below.The following description and Examples are for illustrating theexemplary embodiments, but are not intended to limit the scope of theexemplary embodiments.

The numerical ranges expressed by using “to” in the present disclosureindicate ranges including the numerical values before and after “to” asthe minimum value and the maximum value.

In the numerical ranges described stepwise in the present disclosure,the upper limit or the lower limit of one numerical range may bereplaced by the upper limit or the lower limit of another numericalrange. The upper limit or lower limit of any numerical range describedin the present disclosure may be replaced by a value described inExamples.

In the present disclosure, the term “step” includes not only anindependent step but also a step that cannot be clearly distinguishedfrom other steps but may accomplish an intended purpose.

In the description of exemplary embodiments with reference to thedrawings in the present disclosure, the structures of the exemplaryembodiments are not limited to the structures illustrated in thedrawings. The sizes of members in each figure are schematic, and therelative relationship between the sizes of the members is not limited towhat is illustrated.

In the present disclosure, each component may include two or morecorresponding substances. In the present disclosure, the amount of eachcomponent in a composition refers to, when there are two or moresubstances corresponding to each component in the composition, the totalamount of the substances present in the composition, unless otherwisespecified.

In the present disclosure, each component may include two or more typesof particles corresponding to each component. The particle size of eachcomponent refers to, when there are two or more types of particlescorresponding to each component in the composition, the particle size ofa mixture of two or more types of particles present in the composition,unless otherwise specified.

In the present disclosure, the term “(meth)acrylic” refers to both“acrylic” and “methacrylic”.

In the present disclosure, the “toner for electrostatic charge imagedevelopment” is also referred to simply as “toner”, and the“electrostatic charge image developer” is also referred to simply as a“developer”.

In the present disclosure, a printed material formed by folding arecording medium and bonding the opposing surfaces of the foldedrecording medium to each other or a printed material formed by stackingtwo or more recording media on top of each other and bonding theopposing surfaces of the stacked recording media to each other isreferred to as a “pressure-bonded printed material”. Method forProducing Pressure-Responsive Particles

A method for producing pressure-responsive particles according to anexemplary embodiment includes: an aggregating step of adding anaggregating agent to a dispersion containing composite resin particlescontaining a styrene-based resin including a styrene compound and avinyl monomer other than the styrene compound as polymer components anda (meth)acrylic acid ester-based resin including a (meth)acrylic acidester compound as a polymer component to cause aggregation so as to formaggregated particles A; a shell forming step of adding an aggregatingagent and styrene-based resin particles containing a styrene compoundand a vinyl monomer other than the styrene compound to a dispersioncontaining the aggregated particles A to cause aggregation so as to formaggregated particles B; and a fusing step of heating and fusing theaggregated particles B to form pressure-responsive particles. The amountof the styrene-based resin particles added in the shell forming step is5 mass % or more and 40 mass % or less relative to the total mass of thecomposite resin particles. The amount of the aggregating agent added inthe shell forming step is 0.1 mass % or more and 1.0 mass % or lessrelative to the total mass of the composite resin particles. The massratio of the styrene-based resin to the (meth)acrylic acid ester-basedresin in the pressure-responsive particles is from 80:20 to 20:80. Adifference between the lowest glass transition temperature and thehighest glass transition temperature of resins contained in thepressure-responsive particles is 30° C. or more.

The pressure-responsive particles according to the exemplary embodimentare produced by the method for producing pressure-responsive particlesaccording to the exemplary embodiment.

In the related art, crimped postcards for sales promotion use UV-curablevarnish (UV varnish), and crimped postcards for confidential purposesuse natural rubber-based glue. For both types of postcards, the varnishor glue coating process is complicated, and much effort has beendirected toward dealing with odors and washing the coating device. Forthis, pressure-responsive particles replacing such varnish or glue havebeen studied. Pressure-responsive particles can be taken out as powderas long as the exposure of the (meth)acrylic acid ester-based resin onthe surface is prevented, and the particle size is controlled by using,as a pressure-responsive material, a resin containing a (meth)acrylicacid ester-based resin and a styrene-based resin containing styrene anda vinyl monomer other than styrene as polymer components, wherein themass ratio of the styrene-based resin to the (meth)acrylic acidester-based resin is from 80:20 to 20:80, and a difference between thelowest glass transition temperature and the highest glass transitiontemperature is 30° C. or more.

When pressure-responsive particles are used in a pressure-sensitiveadhesive, the tackiness of the pressure-responsive particles degradeswith time to reduce the shelf life of pre-glued paper for crimpedpostcards. It is thus difficult to manage the inventory of pre-gluedpaper. In contrast, the presence of areas with locally high tackinesscauses sheet tearing at the time of peeling after storage in a highhumidity environment.

The presence of a small area of the core exposed portion on the producedpressure-responsive particles causes aggregation of thepressure-responsive particles and fusion-bonding of thepressure-responsive particles to members in the process of, for example,electrostatic coating of sheets of paper with the pressure-responsiveparticles.

The method for producing pressure-responsive particles according to theexemplary embodiment includes a shell forming step of adding anaggregating agent and styrene-based resin particles containing a styrenecompound and a vinyl monomer other than the styrene compound as polymercomponents to cause aggregation so as to form aggregated particles B,wherein the amount of the aggregating agent added in the shell formingstep is 0.1 mass % or more and 1.0 mass % or less relative to the totalmass of the composite resin particles. In this method, the core and theshell firmly adhere to each other in the pressure-responsive particlesafter completion of aggregation to reduce the area of the core exposedportion. The pressure-responsive particles may thus provide highdispersion storage stability while maintaining tackiness at the time ofpressure bonding and may generate less aggregates and fusion-bondedmaterials.

The pressure-responsive particles according to the exemplary embodimentundergo pressure-induced phase transition because thepressure-responsive particles exhibit the following thermal properties:“having at least two glass transition temperatures, wherein a differencebetween the lowest glass transition temperature and the highest glasstransition temperature is 30° C. or higher”. In the exemplaryembodiment, the pressure-responsive particles that undergopressure-induced phase transition mean pressure-responsive particlesthat satisfy Formula 1 below.

10° C.≤T1−T2   Formula 1

In Formula 1, T1 is a temperature corresponding to a viscosity of 10,000Pas at a pressure of 1 MPa, and T2 is a temperature corresponding to aviscosity of 10,000 Pas at a pressure of 10 MPa. The temperature T1 andthe temperature T2 are determined as described below.

In the method for producing pressure-responsive particles according tothe exemplary embodiment, the mass ratio of the styrene-based resin tothe (meth)acrylic acid ester-based resin in the pressure-responsiveparticles is from 80:20 to 20:80, preferably from 70:30 to 30:70, morepreferably from 60:40 to 40:60 in view of the tackiness at the time ofpressure bonding and the storage stability of the dispersion and toprevent generation of aggregates and fusion-bonded materials.

The styrene-based resin contained in the pressure-responsive particlescontains not only the styrene-based resin contained in the compositeresin particles but also, when the method includes a shell forming step,the styrene-based resin added in the shell forming step.

In the method for producing pressure-responsive particles according tothe exemplary embodiment, a difference between the lowest glasstransition temperature and the highest glass transition temperature ofresins contained in the pressure-responsive particles is 30° C. or more,preferably 40° C. or more, more preferably 60° C. or more, still morepreferably 60° C. or more and 200° C. or less, yet still more preferably80° C. or more and 150° C. or less in view of the tackiness at the timeof pressure bonding and the storage stability of the dispersion and toprevent generation of aggregates and fusion-bonded materials.

The pressure-responsive particles have at least two glass transitiontemperatures, one of which may be the glass transition temperature ofthe styrene-based resin, and the other may be the glass transitiontemperature of the (meth)acrylic acid ester-based resin.

The lowest glass transition temperature in the composite resin particlesmay be the glass transition temperature of the (meth)acrylic acidester-based resin.

The highest glass transition temperature may be the glass transitiontemperature of the styrene-based resin contained in thepressure-responsive particles. In some exemplary embodiments, the lowestglass transition temperature is the glass transition temperature of the(meth)acrylic acid ester-based resin contained in thepressure-responsive particles, and the highest glass transitiontemperature is the glass transition temperature of the styrene-basedresin contained in the pressure-responsive particles.

The lowest glass transition temperature and the highest glass transitiontemperature are of resins present at 1 mass % or more relative to thetotal mass of the resins contained in the pressure-responsive particlesamong the resins contained in the pressure-responsive particles.

The pressure-responsive particles may have three or more glasstransition temperatures or may have two glass transition temperatures.Examples of the form of the pressure-responsive particles having twoglass transition temperatures include pressure-responsive particlescontaining only the styrene-based resin and the (meth)acrylic acidester-based resin; and pressure-responsive particles containing a smallamount of resin other than the styrene-based resin and the (meth)acrylicacid ester-based resin (e.g., the amount of other resin is 5 mass % orless relative to the total mass of the pressure-responsive particles).

In the present disclosure, the glass transition temperatures of theresins are determined from differential scanning calorimetry curves (DSCcurves) obtained by differential scanning calorimetry (DSC). Morespecifically, the glass transition temperature is determined from“extrapolated glass transition onset temperature” described in themethod for determining a glass transition temperature in “TestingMethods for Transition Temperatures of Plastics” in JIS K7121:1987.

The glass transition temperature of the styrene-based resin contained inthe pressure-responsive particles is preferably 30° C. or higher, morepreferably 40° C. or higher, still more preferably 50° C. or higher inorder to prevent fluidization of the composite resin particles under nopressure, and preferably 110° C. or lower, more preferably 100° C. orlower, still more preferably 90° C. or lower in order to form compositeresin particles that easily undergo pressure-induced phase transition.

The glass transition temperature of the (meth)acrylic acid ester-basedresin contained in the pressure-responsive particles is preferably 10°C. or lower, more preferably 0° C. or lower, still more preferably −10°C. or lower in order to form pressure-responsive resin particles thateasily undergo pressure-induced phase transition, and preferably −90° C.or higher, more preferably −80° C. or higher, still more preferably −70°C. or higher in order to prevent fluidization of the pressure-responsiveresin particles under no pressure.

Aggregating Step

The method for producing pressure-responsive particles according to theexemplary embodiment includes an aggregating step of adding anaggregating agent to a dispersion containing composite resin particlescontaining a styrene-based resin including a styrene compound and avinyl monomer other than the styrene compound as polymer components anda (meth)acrylic acid ester-based resin including a (meth)acrylic acidester compound as a polymer component to cause aggregation so as to formaggregated particles A.

The details of the styrene-based resin and the (meth)acrylic acidester-based resin will be described below.

In the method for producing pressure-responsive particles according tothe exemplary embodiment, the pressure-responsive particles are producedby an aggregation-coalescence method.

In the aggregating step, the composite resin particles aggregate in adispersion containing the composite resin particles to form aggregatedparticles A having a size closer to the intended size of thepressure-responsive particles.

Specifically, the aggregated particles are formed, for example, asfollows: adding an aggregating agent to a composite resin particledispersion and adjusting the pH of the composite resin particledispersion to the acid side (e.g., pH 2 or higher and pH 5 or lower),and adding a dispersion stabilizer as desired; and then heating thedispersion to a temperature close to the glass transition temperature ofthe styrene-based resin (specifically, for example, the glass transitiontemperature of the styrene-based resin −10° C. or higher and the glasstransition temperature +15° C. or lower) to aggregate the compositeresin particles.

The aggregating step may involve adding an aggregating agent to thecomposite resin particle dispersion at room temperature (e.g., 25° C.)under stirring with a rotary shear homogenizer and adjusting the pH ofthe composite resin particle dispersion to the acid side (e.g., pH 2 orhigher and pH 5 or lower), and heating the dispersion after adding adispersion stabilizer as desired.

Examples of the aggregating agent include surfactants having polarityopposite to the polarity of a surfactant contained in the dispersioncomposite resin particle dispersion, inorganic metal salts, and divalentor higher valent metal complexes. The use of a metal complex as anaggregating agent reduces the amount of the surfactant used and improvescharging characteristics.

Examples of inorganic metal salts include metal salts, such as calciumchloride, calcium nitrate, barium chloride, magnesium chloride, zincchloride, aluminum chloride, and aluminum sulfate; and inorganic metalsalt polymers, such as polyaluminum chloride, polyaluminum hydroxide,and calcium polysulfide.

Of these, aluminum-containing aggregating agents are preferred, aluminumchloride, aluminum sulfate, polyaluminum chloride, or polyaluminumhydroxide are more preferred, and aluminum sulfate is still morepreferred in view of the tackiness at the time of pressure bonding andthe storage stability of the dispersion and to prevent generation ofaggregates and fusion-bonded materials.

The amount of the aggregating agent added is not limited, but preferably0.1 parts by mass or more and 5 parts by mass or less, more preferably0.2 parts by mass or more and 2 parts by mass or less, relative to 100parts by mass of the composite resin particles.

The volume average particle size of the composite resin particles ispreferably 140 nm or more and 350 nm or less, more preferably 180 nm ormore and 320 nm or less, still more preferably 200 nm or more and 300 nmor less.

The dispersion containing the composite resin particles in theaggregating step is preferably a water-based dispersion, more preferablya water dispersion.

The amount of the composite resin particles in the dispersion containingthe composite resin particles is preferably 20 mass % or more and 50mass % or less, more preferably 30 mass % or more and 40 mass % or less.

In the aggregating step, silica particles may further be added in viewof the tackiness at the time of pressure bonding and the storagestability of the dispersion.

When a dispersion containing silica particles is added, the silicaparticles catch (trap) the aggregating agent after completion ofaggregation in the shell forming step to prevent the aggregating agentfrom remaining in the pressure-responsive particles. Thus, theaggregating agent does not inhibit mixing of the styrene-based resin andthe (meth)acrylic acid ester-based resin during formation of thepressure-responsive particles, which may provide high dispersion storagestability while maintaining tackiness at the time of pressure bonding.In particular, it is effective to remove an excess of the aggregatingagent since the aggregating agent is added in the shell forming step.

The silica particles are preferably added by using a dispersioncontaining silica particles.

The dispersion containing silica particles is preferably a dispersion ofsilica particles in a water-based medium, more preferably a dispersionof silica particles in water.

Examples of the dispersion medium include water-based media includingwater and alcohols. These media may be used alone or in combination oftwo or more.

The amount of the silica particles added in the aggregating step ispreferably 0.5 mass % or more and 10 mass % or less, more preferably 1mass % or more and 9 mass % or less, still more preferably 2 mass % ormore and 8 mass % or less relative to the total mass of the compositeresin particles in view of the tackiness at the time of pressure bondingand the storage stability of the dispersion.

The solid content of the dispersion containing the silica particles isnot limited, but preferably 1 mass % or more and 50 mass % or less, morepreferably 2 mass % or more and 40 mass % or less.

In view of the tackiness at the time of pressure bonding and the storagestability of the dispersion, the arithmetic mean particle size of thesilica particles is preferably 5 nm or more and 100 nm or less, morepreferably 6 nm or more and 80 nm or less, still more preferably 7 nm ormore and 40 nm or less, yet still more preferably 7 nm or more and 25 nmor less.

The arithmetic mean particle size of the silica particles in theexemplary embodiment is determined by capturing the images of the silicaparticles through observation with a scanning electron microscope(S-4100 available from Hitachi, Ltd). The captured images are loadedinto an image analyzer (LUZEXIII available from Nireco Corporation). Thearea of each particle is determined by image analysis, and theequivalent circular diameter (nm) is calculated from the area. Thearithmetic mean of the equivalent circular diameters of 100 or moreparticles is taken as an arithmetic mean particle size.

Shell Forming Step

The method for producing pressure-responsive particles according to theexemplary embodiment includes a shell forming step of adding anaggregating agent and styrene-based resin particles containing a styrenecompound and a vinyl monomer other than the styrene compound as polymercomponents to a dispersion containing the aggregated particles A formedin the aggregating step to cause aggregation so as to form aggregatedparticles B. The amount of the styrene-based resin particles added inthe shell forming step is 5 mass % or more and 40 mass % or lessrelative to the total mass of the composite resin particles. The amountof the aggregating agent added in the shell forming step is 0.1 mass %or more and 1.0 mass % or less relative to the total mass of thecomposite resin particles.

Specifically, for example, an aggregating agent and a styrene-basedresin particle dispersion are added to a dispersion containing theaggregated particles A after the aggregating step, and the dispersionmixture is then heated to a temperature close to the glass transitiontemperature of the styrene-based resin (specifically, for example, theglass transition temperature of the styrene-based resin −10° C. orhigher and the glass transition temperature +15° C. or lower) toaggregate the styrene-based resin particles on the surfaces of theaggregated particles A so as to form aggregated particles B having thestyrene-based resin particles on the surfaces.

The styrene-based resin particles are preferably added by using thestyrene-based resin particle dispersion in the shell forming step. Anexemplary aspect of the styrene-based resin particle dispersion in theshell forming step is the same as an exemplary aspect of thestyrene-based resin particle dispersion in the aggregating step.

The amount of the styrene-based resin particles added in the shellforming step is 5 mass % or more and 40 mass % or less, preferably 10mass % or more and 30 mass % or less, more preferably 12 mass % or moreand 25 mass % or less, still more preferably 15 mass % or more and 20mass % or less relative to the total mass of the composite resinparticles used in the aggregating step in view of the tackiness at thetime of pressure bonding and the storage stability of the dispersion andto prevent generation of aggregates and fusion-bonded materials.

The amount of the aggregating agent in the shell forming step is 0.1mass % or more and 1.0 mass % or less, preferably 0.3 mass % or more and0.98 mass % or less, more preferably 0.4 mass % or more and 0.8 mass %or less relative to the total mass of the composite resin particles usedin the aggregating step in view of the tackiness at the time of pressurebonding and the storage stability of the dispersion and to preventgeneration of aggregates and fusion-bonded materials.

In the shell forming step, the styrene-based resin particles and theaggregating agent may be added after the liquid temperature of thedispersion containing the aggregated particles A is lowered after theaggregating step in view of the tackiness at the time of pressurebonding and the storage stability of the dispersion and to preventgeneration of aggregates and fusion-bonded materials. The liquidtemperature of the dispersion may be lowered by 5° C. or more.

An exemplary aspect of the aggregating agent used in the shell formingstep is the same as an exemplary aspect of the aggregating agent used inthe aggregating step.

The aggregating agent used in the shell forming step may be the same asor different from the aggregating agent used in the aggregating step. Insome exemplary embodiments, the aggregating agent used in the shellforming step is different from the aggregating agent used in theaggregating step.

The pressure-responsive particles having a core-shell structure obtainedafter the shell forming step and the fusing step have a shell layercontaining a styrene-based resin. In addition to the styrene-based resinparticle dispersion, a resin particle dispersion in which another typeof resin particles are dispersed may be used to form a shell layercontaining another type of resin particles.

Fusing Step

The method for producing pressure-responsive particles according to theexemplary embodiment includes a fusing step of heating and fusing theaggregated particles B to form pressure-responsive particles.

In the fusing step, the aggregated particle dispersion in which theaggregated particles B are dispersed is heated to, for example, atemperature equal to or higher than the glass transition temperature ofthe styrene resin particles (e.g., a temperature equal to or higher thanthe glass transition temperature of the styrene resin by 30° C. to 50°C.) to fuse and coalesce the aggregated particles intopressure-responsive particles.

After completion of the fusing step, the pressure-responsive particlesformed in the dispersion are subjected to a known washing step, a knownsolid-liquid separation step, and a known drying step to provide drypressure-responsive particles. The washing step may involve sufficientdisplacement washing with ion exchange water in view of chargingcharacteristics. The solid-liquid separation step may involve, forexample, suction filtration or pressure filtration in view ofproductivity. The drying step may involve, for example, freeze drying,flush drying, fluidized bed drying, or vibratory fluidized bed drying inview of productivity.

The pressure-responsive particles may be produced by, for example,adding external additives to the obtained dry pressure-responsiveparticles and mixing them. Mixing may be performed with, for example, aV-blender, a Henschel mixer, or a Lodige mixer. In addition, coarseparticles in the pressure-responsive particles may be removed with, forexample, a vibratory sifter, or a wind sifter, as desired.

The pressure-responsive particles may contain a colorant, a releaseagent, and other additives as desired. When the pressure-responsiveparticles contain a colorant and a release agent, the aggregating stepis performed by using a mixture of a composite resin particledispersion, a colorant particle dispersion, and a release agent particledispersion, followed by the fusing step. The colorant particledispersion and the release agent particle dispersion can be prepared by,for example, mixing materials and then subjecting the mixture to adispersion treatment using a known disperser.

The method for producing pressure-responsive particles according to theexemplary embodiment may further include a polymerization step B ofpolymerizing a styrene compound and a vinyl monomer other than thestyrene compound to form a styrene-based resin, and a polymerizationstep B of polymerizing a (meth)acrylic acid ester compound in thepresence of the styrene-based resin obtained in the polymerization stepA to form composite resin particles containing the styrene-based resinand a (meth)acrylic acid ester-based resin.

Polymerization Step A

The method for producing a pressure-responsive particle dispersionaccording to the exemplary embodiment may further include apolymerization step A of polymerizing a styrene compound and a vinylmonomer other than the styrene compound to form a styrene-based resin.

The polymerization in the polymerization step A is not limited and maybe emulsion polymerization.

The method for producing a composite resin particle dispersion mayinvolve emulsion polymerization.

The polymerization step A is preferably a step of forming styrene-basedresin particles, more preferably a step of forming a styrene-based resinparticle dispersion.

One method for dispersing styrene-based resin particles in a dispersionmedium involves, for example, stirring a mixture of a styrene-basedresin and a dispersion medium with a rotary shear homogenizer, a ballmill having media, a sand mill, or Dyno-Mill to form a dispersion.

Another method for dispersing styrene-based resin particles in adispersion medium is emulsion polymerization. Specifically, emulsionpolymerization involves mixing polymer components of the styrene-basedresin with a chain transfer agent or a polymerization initiator, thenfurther mixing the mixture with a water-based medium containing asurfactant under stirring to form an emulsion, and polymerizing astyrene-based resin in the emulsion. In this case, the chain transferagent is preferably a thiol compound, more preferably dodecane thiol.

Examples of the dispersion medium include water-based media describedabove.

Examples of the surfactant include anionic surfactants, such as sulfateester salts, sulfonate salts, phosphate esters, and soaps; cationicsurfactants, such as amine salts and quaternary ammonium salts; andnonionic surfactants, such as polyethylene glycols, alkylphenol ethyleneoxide adducts, and polyhydric alcohols. A nonionic surfactant may beused in combination with an anionic surfactant or a cationic surfactant.Of these surfactants, an anionic surfactant may be used. The surfactantmay be used alone or in combination of two or more.

Examples of the polymerization initiator include, but are not limitedto, known photopolymerization initiators and known thermalpolymerization initiators.

Of these, thermal polymerization initiators are preferred, peroxides aremore preferred, and ammonium persulfate is still more preferred.

The polymerization temperature and the polymerization time are notlimited and appropriately selected to according to, for example, themonomers and the polymerization initiator used.

In the polymerization step A, the volume average particle size of thestyrene-based resin particles to be dispersed in the styrene-based resinparticle dispersion is preferably 100 nm or more and 250 nm or less,more preferably 120 nm or more and 220 nm or less, still more preferably150 nm or more and 200 nm or less.

The volume average particle size (D50v) of the resin particles containedin the resin particle dispersion refers to the particle size at 50%cumulative volume from the smallest particle size in the volume-basedparticle size distribution obtained by measuring particle sizes with alaser diffraction particle size distribution analyzer (e.g., LA-700available from Horiba Ltd).

The amount of the styrene-based resin particles in the styrene-basedresin particle dispersion is not limited, but preferably 30 mass % ormore and 60 mass % or less, more preferably 40 mass % or more and 50mass % or less. Polymerization Step B

The method for producing a pressure-responsive particle dispersionaccording to the exemplary embodiment may further include apolymerization step B of polymerizing a (meth)acrylic acid estercompound in the presence of the styrene-based resin obtained in thepolymerization step A to form composite resin particles containing thestyrene-based resin and a (meth)acrylic acid ester-based resin.

The polymerization step B may be a step of forming a composite resinparticle dispersion.

One method for dispersing composite resin particles in a dispersionmedium involves, for example, stirring a mixture of a styrene-basedresin and a dispersion medium with a rotary shear homogenizer, a ballmill having media, a sand mill, or Dyno-Mill to form a dispersion.

Another method for dispersing the composite resin particles in adispersion medium involves adding polymer components of the(meth)acrylic acid ester-based resin to a styrene-based resin particledispersion and adding a water-based medium as desired. Next, while thedispersion is gently stirred, the temperature of the dispersion israised to the glass transition temperature of the produced styrene-basedresin or higher (e.g., a temperature higher than the glass transitiontemperature of the styrene-based resin by 10° C. to 30° C.). Next, whilethe temperature is maintained, a water-based medium containing apolymerization initiator is slowly added dropwise, and stirring isfurther continued for a long time in the range of 1 hour or more and 15hours or less. In this case, ammonium persulfate may be used as apolymerization initiator.

Examples of the dispersion medium and the polymerization initiator mayinclude those described above.

The polymerization step B may use a surfactant. Examples of thesurfactant may include those described above.

The polymerization temperature and the polymerization time are notlimited and appropriately selected to according to, for example, themonomers and the polymerization initiator used.

Although the details of the mechanism are unclear, the use of the abovemethod may cause impregnation of the styrene-based resin particles withthe monomers and the polymerization initiator to polymerize the(meth)acrylic acid ester inside the styrene-based resin particles. Thismethod may produce composite resin particles in which the (meth)acrylicacid ester-based resin is contained in the styrene-based resinparticles, in which the styrene-based resin and the (meth)acrylic acidester-based resin form a microphase-separated structure.

The method for producing pressure-responsive particles according to theexemplary embodiment may include a known step other than the stepsdescribed above.

The details of the styrene-based resin and the (meth)acrylic acidester-based resin in the exemplary embodiment will be described below.

Styrene-Based Resin

The styrene-based resin contained in the pressure-responsive particlescontains a styrene compound and a vinyl monomer other than the styrenecompound as polymer components.

The styrene compound used to synthesize the styrene-based resin mayinclude styrene.

The mass percentage of styrene relative to the total mass of the polymercomponents of the styrene-based resin is preferably 60 mass % or more,more preferably 70 mass % or more, still more preferably 75 mass % ormore in order to prevent fluidization of the pressure-responsiveparticles under no pressure, and preferably 95 mass % or less, morepreferably 90 mass % or less, still more preferably 85 mass % or less inorder to form pressure-responsive particles that easily undergopressure-induced phase transition.

Examples of styrene compounds other than styrene used to synthesize thestyrene-based resin include vinyl naphthalene; alkyl-substitutedstyrenes, such as α-methylstyrene, o-methylstyrene, m-methylstyrene,p-methylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-n-butylstyrene,p-tert-butylstyrene, p-n-hexylstyrene, p-n-octylstyrene,p-n-nonylstyrene, p-n-decylstyrene, and p-n-dodecylstyrene;aryl-substituted styrenes, such as p-phenylstyrene; alkoxy-substitutedstyrenes, such as p-methoxystyrene; halogen-substituted styrenes, suchas p-chlorostyrene, 3,4-dichlorostyrene, p-fluorostyrene, and2,5-difluorostyrene; and nitro-substituted styrenes, such asm-nitrostyrene, o-nitrostyrene, and p-nitrostyrene. The styrene compoundmay be used alone or in combination of two or more.

Examples of the vinyl monomer other than the styrene compound used tosynthesize the styrene-based resin include an acrylic monomer.

The acrylic monomer may be at least one acrylic monomer selected fromthe group consisting of (meth)acrylic acid and (meth)acrylic acid estercompounds. Examples of (meth)acrylic acid ester compounds include(meth)acrylic acid alkyl ester compounds, (meth)acrylic acidcarboxy-substituted alkyl ester compounds, (meth)acrylic acidhydroxy-substituted alkyl ester compounds, (meth)acrylic acidalkoxy-substituted alkyl ester compounds, and di(meth)acrylic acid estercompounds. The acrylic monomer may be used alone or in combination oftwo or more.

Examples of (meth)acrylic acid alkyl ester compounds include methyl(meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl(meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl(meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth)acrylate,stearyl (meth)acrylate, cyclohexyl (meth) acrylate, dicyclopentanyl(meth) acrylate, and isobornyl (meth) acrylate.

Examples of (meth)acrylic acid carboxy-substituted alkyl esters include2-carboxyethyl (meth)acrylate.

Examples of (meth)acrylic acid hydroxy-substituted alkyl ester compoundsinclude 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth) acrylate,3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate,3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth) acrylate.

Examples of (meth)acrylic acid alkoxy-substituted alkyl ester compoundsinclude 2-methoxyethyl (meth)acrylate.

Examples of di(meth)acrylic acid ester compounds include ethylene glycoldi(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycoldi(meth)acrylate, butanediol di(meth)acrylate, pentanedioldi(meth)acrylate, hexanediol di(meth)acrylate, nonanedioldi(meth)acrylate, and decanediol di(meth)acrylate.

Examples of (meth)acrylic acid ester compounds include2-(diethylamino)ethyl (meth)acrylate, benzyl (meth)acrylate, and methoxypolyethylene glycol (meth)acrylate.

Examples of the vinyl monomer other than the styrene compound used tosynthesize the styrene-based resin include (meth)acrylonitrile; vinylethers, such as vinyl methyl ether and vinyl isobutyl ether; vinylketones, such as vinyl methyl ketone, vinyl ethyl ketone, and vinylisopropenyl ketone; and olefins, such as isoprene, butene, andbutadiene.

To form pressure-responsive particles that easily undergopressure-induced phase transition, the styrene-based resin preferablycontains a (meth)acrylic acid ester compound as a polymer component,more preferably contains a (meth)acrylic acid alkyl ester compound as apolymer component, still more preferably contains a (meth)acrylic acidalkyl ester compound with a C2-C10 alkyl group, yet still morepreferably contains a (meth)acrylic acid alkyl ester compound with aC4-C8 alkyl group, yet still more preferably contains at least one ofn-butyl acrylate and 2-ethylhexyl acrylate.

To form pressure-responsive particles that easily undergopressure-induced phase transition, the vinyl monomer present at thehighest mass percentage in the styrene-based resin among vinyl monomersother than styrene is preferably a (meth)acrylic acid ester, morepreferably a (meth)acrylic acid alkyl ester compound, still morepreferably a (meth)acrylic acid alkyl ester compound with a C2-C10 alkylgroup, yet still more preferably n-butyl acrylate or 2-ethylhexylacrylate.

The mass percentage of the (meth)acrylic acid ester compound relative tothe total mass of the polymer components of the styrene-based resin ispreferably 40 mass % or less, more preferably 30 mass % or less, stillmore preferably 25 mass % or less in order to prevent fluidization ofthe pressure-responsive particles under no pressure, and preferably 5mass % or more, more preferably 10 mass % or more, still more preferably15 mass % or more in order to facilitate the pressure-induced phasetransition of the pressure-responsive particles. The (meth)acrylic acidester compound is preferably a (meth)acrylic acid alkyl ester compound,more preferably a (meth)acrylic acid alkyl ester compound with a C2-C10alkyl group, still more preferably a (meth)acrylic acid alkyl estercompound with a C4-C8 alkyl group.

The styrene-based resin may contain at least one of n-butyl acrylate and2-ethylhexyl acrylate as a polymer component. The total amount ofn-butyl acrylate and 2-ethylhexyl acrylate relative to the total amountof the polymer components of the styrene-based resin is preferably 40mass % or less, more preferably 30 mass % or less, still more preferably25 mass % or less in order to prevent fluidization of thepressure-responsive particles under no pressure, and preferably 5 mass %or more, more preferably 10 mass % or more, still more preferably 15mass % or more in order to form pressure-responsive particles thateasily undergo pressure-induced phase transition.

The weight average molecular weight of the styrene-based resin ispreferably 10,000 or more, more preferably 20,000 or more, still morepreferably 30,000 or more in order to prevent fluidization of thepressure-responsive particles under no pressure, and preferably 200,000or less, more preferably 150,000 or less, still more preferably 100,000or less in order to form pressure-responsive particles that easilyundergo pressure-induced phase transition.

In the present disclosure, the weight average molecular weights of theresins are determined by gel permeation chromatography (GPC). Themeasurement of the molecular weights by GPC is carried out by usingHLC-8120GPC available from Tosoh Corporation as a GPC system, TSKgelSuperHM-M (15 cm) available from Tosoh Corporation as a column, andtetrahydrofuran as a solvent. The weight average molecular weights ofthe resins are calculated from molecular weight calibration curves madeby using a monodisperse polystyrene standard.

The glass transition temperature of the styrene-based resin ispreferably 30° C. or higher, more preferably 40° C. or higher, stillmore preferably 50° C. or higher in order to prevent fluidization of thepressure-responsive particles under no pressure, and preferably 110° C.or lower, more preferably 100° C. or lower, still more preferably 90° C.or lower in order to form pressure-responsive particles that easilyundergo pressure-induced phase transition. (Meth)acrylic AcidEster-Based Resin

The (meth)acrylic acid ester-based resin contained in thepressure-responsive particles may contain a (meth)acrylic acid estercompound as a polymer component.

The (meth)acrylic acid ester compound may be used alone or incombination of two or more. At least two (meth)acrylic acid esters maybe contained as polymer components.

The mass percentage of the (meth)acrylic acid ester relative to thetotal mass of the polymer components of the (meth)acrylic acidester-based resin is 90 mass % or more, more preferably 95 mass % ormore, still more preferably 98 mass % or more, yet still more preferably100 mass %.

Examples of (meth)acrylic acid ester compounds used to synthesize the(meth)acrylic acid ester-based resin include (meth)acrylic acid alkylester compounds, (meth)acrylic acid carboxy-substituted alkyl estercompounds, (meth)acrylic acid hydroxy-substituted alkyl ester compounds,(meth)acrylic acid alkoxy-substituted alkyl ester compounds, anddi(meth)acrylic acid ester compounds.

Examples of (meth)acrylic acid alkyl ester compounds include methyl(meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl(meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl(meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth)acrylate,stearyl (meth)acrylate, cyclohexyl (meth) acrylate, dicyclopentanyl(meth) acrylate, and isobornyl (meth) acrylate.

Examples of (meth)acrylic acid carboxy-substituted alkyl ester compoundsinclude 2-carboxyethyl (meth)acrylate.

Examples of (meth)acrylic acid hydroxy-substituted alkyl ester compoundsinclude 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth) acrylate,3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate,3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth) acrylate.

Examples of (meth)acrylic acid alkoxy-substituted alkyl ester compoundsinclude 2-methoxyethyl (meth)acrylate.

Examples of di(meth)acrylic acid ester compounds include ethylene glycoldi(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycoldi(meth)acrylate, butanediol di(meth)acrylate, pentanedioldi(meth)acrylate, hexanediol di(meth)acrylate, nonanedioldi(meth)acrylate, and decanediol di(meth)acrylate.

Examples of (meth)acrylic acid ester compounds include2-(diethylamino)ethyl (meth)acrylate, benzyl (meth)acrylate, and methoxypolyethylene glycol (meth)acrylate.

The (meth)acrylic acid ester compound used to synthesize the(meth)acrylic acid ester-based resin is preferably a (meth)acrylic acidalkyl ester compound, more preferably a (meth)acrylic acid alkyl estercompound with a C2-C10 alkyl group, still more preferably a(meth)acrylic acid alkyl ester compound with a C4-C8 alkyl group, yetstill more preferably n-butyl acrylate or 2-ethylhexyl acrylate in orderto form pressure-responsive particles that easily undergopressure-induced phase transition and have good adhesiveness.

To form pressure-responsive particles that easily undergopressure-induced phase transition, the styrene-based resin and the(meth)acrylic acid ester-based resin contained in thepressure-responsive particles may contain the same (meth)acrylic acidester compound as a polymer component. In other words, to formpressure-responsive particles that easily undergo pressure-induced phasetransition, the styrene-based resin and the (meth)acrylic acidester-based resin contained in the pressure-responsive particles mayeach have a structural unit derived from the same (meth)acrylic acidester compound.

Two (meth)acrylic acid ester compounds present at the highest two masspercentages among at least two (meth)acrylic acid ester compoundscontained as polymer components in the (meth)acrylic acid ester-basedresin may be (meth)acrylic acid alkyl ester compounds. The (meth)acrylicacid alkyl ester compounds are preferably (meth)acrylic acid alkyl estercompounds with a C2-C10 alkyl group, more preferably (meth)acrylic acidalkyl ester compounds with a C4-C8 alkyl group.

When two (meth)acrylic acid ester compounds present at the highest twomass percentages among at least two (meth)acrylic acid ester compoundscontained as polymer components in the (meth)acrylic acid ester-basedresin are (meth)acrylic acid alkyl ester compounds, a difference innumber of carbon atoms between the alkyl groups of the two (meth)acrylicacid alkyl ester compounds is preferably 1 or more and 4 or less, morepreferably 2 or more and 4 or less, still more preferably 3 or 4 inorder to form pressure-responsive particles that easily undergopressure-induced phase transition and have better tackiness.

To form pressure-responsive particles that easily undergopressure-induced phase transition and have better tackiness, the(meth)acrylic acid ester-based resin preferably contains n-butylacrylate and 2-ethylhexyl acrylate as polymer components, and morepreferably two (meth)acrylic acid ester compounds present at the highesttwo mass percentages among at least two (meth)acrylic acid estercompounds contained as polymer components in the (meth)acrylic acidester-based resin may be n-butyl acrylate and 2-ethylhexyl acrylate. Thetotal amount of n-butyl acrylate and 2-ethylhexyl acrylate relative tothe total amount of the polymer components of the (meth)acrylic acidester-based resin is preferably 90 mass % or more, more preferably 95mass % or more, still more preferably 98 mass % or more, yet still morepreferably 100 mass %.

The (meth)acrylic acid ester-based resin may contain, as a polymercomponent, a vinyl monomer other than (meth)acrylic acid estercompounds. Examples of the vinyl monomer other than (meth)acrylic acidesters include (meth)acrylic acid; styrene; styrene-based monomers otherthan styrene; (meth)acrylonitrile; vinyl ethers, such as vinyl methylether and vinyl isobutyl ether; vinyl ketones, such as vinyl methylketone, vinyl ethyl ketone, and vinyl isopropenyl ketone; and olefins,such as isoprene, butene, and butadiene. These vinyl monomers may beused alone or in combination of two or more.

When the (meth)acrylic acid ester-based resin contains, as a polymercomponent, a vinyl monomer other than (meth)acrylic acid estercompounds, the vinyl monomer other than (meth)acrylic acid estercompounds is preferably at least one of acrylic acid and methacrylicacid, more preferably acrylic acid.

The weight average molecular weight of the (meth)acrylic acidester-based resin is preferably 10,000 or more, more preferably 20,000or more, still more preferably 30,000 or more in order to preventfluidization of the pressure-responsive particles under no pressure, andpreferably 200,000 or less, more preferably 150,000 or less, still morepreferably 100,000 or less in order to form pressure-responsiveparticles that easily undergo pressure-induced phase transition.

The glass transition temperature of the (meth)acrylic acid ester-basedresin is preferably 10° C. or lower, more preferably 0° C. or lower,still more preferably −10° C. or lower in order to formpressure-responsive particles that easily undergo pressure-induced phasetransition, and preferably −90° C. or higher, more preferably −80° C. orhigher, still more preferably −70° C. or higher in order to preventfluidization of the pressure-responsive particles under no pressure.

Other Resins

The pressure-responsive particles may contain, for example, polystyrene;and non-vinyl resins, such as epoxy resins, polyester resins,polyurethane resins, polyamide resins, cellulose resins, polyetherresins, and modified rosins. These resins may be used alone or incombination of two or more.

Various Additives

The pressure-responsive particles may contain, as desired, colorants(e.g., pigments, dyes), release agents (e.g., hydrocarbon waxes; naturalwaxes, such as carnauba wax, rice wax, and candelilla wax; synthetic ormineral and petroleum waxes, such as montan wax; and ester waxes, suchas waxes of fatty acid esters and montanic acid esters), and chargecontrol agents.

When the pressure-responsive particles are transparent resin particles,the amount of colorant in the pressure-responsive particles relative tothe total amount of the pressure-responsive particles is preferably 1.0mass % or less, more preferably as low as possible in order to improvethe transparency of the pressure-responsive particles.

The other resins and the additives may be added to the dispersioncontaining the composite resin particles in the aggregating step so thatthey are contained in the pressure-responsive particles.

Structure of Pressure-Responsive Particles

The internal structure of the pressure-responsive particles may be asea-island structure. The sea-island structure may have a sea phasecontaining a styrene-based resin and island phases dispersed in the seaphase and containing a (meth)acrylic acid ester-based resin. A specificform of the styrene-based resin contained in the sea phase is asdescribed above. A specific form of the (meth)acrylic acid ester-basedresin contained in the island phases is as described above. Islandphases free of the (meth)acrylic acid ester-based resin may be dispersedin the sea phase.

When the pressure-responsive particles have a sea-island structure, theisland phases may have an average size of 200 nm or more and 500 nm orless. When the island phases have an average size of 500 nm or less, thepressure-responsive particles easily undergo pressure-induced phasetransition. When the island phases have an average size of 200 nm ormore, the pressure-responsive particles have desired mechanical strength(e.g., strength resistant to deformation during stirring in a developingdevice). From these viewpoints, the island phases preferably have anaverage size of 220 nm or more and 450 nm or less, more preferably havean average size of 250 nm or more and 400 nm or less.

Examples of the method for controlling the average size of the islandphases in the sea-island structure in the above range include increasingor reducing the amount of the (meth)acrylic acid ester-based resinrelative to the amount of the styrene-based resin or increasing orreducing the length of time for maintaining a high temperature in thestep of fusing and coalescing the aggregated resin particles in themethod for producing pressure-responsive particles described below.

The observation of the sea-island structure and the measurement of theaverage size of the island phases are carried out by the followingmethods.

The pressure-responsive particles are embedded in epoxy resin and cutwith a diamond knife or the like to prepare a section. The preparedsection is stained with osmium tetroxide or ruthenium tetroxide in adesiccator. The stained section is observed with a scanning electronmicroscope (SEM). The sea phase and the island phases of the sea-islandstructure are distinguished by shades of color resulting from the degreeof staining of the resins with osmium tetroxide or ruthenium tetroxide.Whether the sea-island structure is present is confirmed by using thismethod. From the SEM image, 100 island phases are randomly selected. Themajor axis of each island phase is measured, and the average value of100 major axes is defined as the average size.

The pressure-responsive particles may be pressure-responsive particleshaving a single-layer structure, or may be core-shellpressure-responsive particles having a core and a shell layer coatingthe core. To prevent fluidization of the pressure-responsive particlesunder no pressure, the pressure-responsive particles may be core-shellpressure-responsive particles.

When the pressure-responsive particles have a core-shell structure, thecore may contain a styrene-based resin and a (meth)acrylic acidester-based resin in order to facilitate pressure-induced phasetransition. The shell layer may contain a styrene-based resin in orderto prevent fluidization of the pressure-responsive particles under nopressure. A specific form of the styrene-based resin is as describedabove. A specific form of the (meth)acrylic acid ester-based resin is asdescribed above.

When the pressure-responsive particles have a core-shell structure, thecore may have a sea phase containing a styrene-based resin and islandphases dispersed in the sea phase and containing a (meth)acrylic acidester-based resin. The average size of the island phases may be in theabove range. In addition to the core having the above configuration, theshell layer may contain a styrene-based resin. In this case, the seaphase of the core and the shell layer are continuously formed, and thepressure-responsive particles thus easily undergo pressure-induced phasetransition. A specific form of the styrene-based resin contained in thesea phase of the core and the shell layer is as described above. Aspecific form of the (meth)acrylic acid ester-based resin contained inthe island phases of the core is as described above.

Examples of the resin contained in the shell layer include polystyrene;and non-vinyl resins, such as epoxy resins, polyester resins,polyurethane resins, polyamide resins, cellulose resins, polyetherresins, and modified rosins. These resins may be used alone or incombination of two or more.

The average thickness of the shell layer is preferably 120 nm or more,more preferably 130 nm or more, still more preferably 140 nm or more inorder to prevent deformation of the pressure-responsive particles, andpreferably 550 nm or less, more preferably 500 nm or less, still morepreferably 400 nm or less in order to facilitate the pressure-inducedphase transition of the pressure-responsive particles.

The average thickness of the shell layer is measured by the followingmethod.

The pressure-responsive particles are embedded in epoxy resin and cutwith a diamond knife or the like to prepare a section. The preparedsection is stained with osmium tetroxide or ruthenium tetroxide in adesiccator. The stained section is observed with a scanning electronmicroscope (SEM). From the SEM image, 10 pressure-responsive particlesare randomly selected. The thickness of the shell layer is measured at20 points per pressure-responsive particle, and the average value iscalculated. The average value for 10 pressure-responsive particles isdefined as the average thickness.

The volume average particle size (D50v) of the pressure-responsiveparticles is preferably 4 μm or more, more preferably 5 μm or more,still more preferably 6 μm or more in order to make it easy to handlethe pressure-responsive particles, and preferably 30 μm or less, morepreferably 20 μm or less, still more preferably 15 μm or less in orderto facilitate the pressure-induced phase transition of the entirepressure-responsive particles.

The volume average particle size (D50v) of the pressure-responsiveparticles is measured by using Coulter Multisizer II (available fromBeckman Coulter, Inc.) with an aperture having a diameter of 100 μm. To2 mL of a 5 mass % aqueous solution of sodium alkylbenzene sulfonate,0.5 mg or more and 50 mg or less of the pressure-responsive particlesare added and dispersed. The resulting dispersion is next mixed with 100mL or more and 150 mL or less of an electrolyte (ISOTON-II availablefrom Beckman Coulter Inc.). The resulting mixture is subjected to adispersion treatment with an ultrasonic disperser for 1 minute, and theobtained dispersion is used as a sample. The particle sizes of 50,000particles having particle sizes of 2 μm or more and 60 μm or less in thesample are measured. The particle size at 50% cumulative volume from thesmallest particle size in the volume-based particle size distribution isdefined as a volume average particle size (D50v).

External Additives

The pressure-responsive particles may contain external additives asdesired.

Examples of external additives include inorganic particles. Examples ofthe inorganic particles include SiO₂, TiO₂, Al₂O₃, CuO, ZnO, SnO₂, CeO₂,Fe₂O₃, MgO, BaO, CaO, K₂O, Na₂O, ZrO₂, CaO.SiO₂, K₂O.(TiO₂)_(n),Al₂O₃.2SiO₂, CaCO₃, MgCO₃, BaSO₄, and MgSO₄.

The surfaces of the inorganic particles serving as an external additivemay be hydrophobized. Hydrophobization is performed by, for example,immersing the inorganic particles in a hydrophobizing agent. Examples ofthe hydrophobizing agent include, but are not limited to, a silanecoupling agent, a silicone oil, a titanate coupling agent, and analuminum coupling agent. These hydrophobizing agents may be used aloneor in combination of two or more. The amount of the hydrophobizing agentis, for example, 1 part by mass or more and 10 parts by mass or lessrelative to 100 parts by mass of the inorganic particles.

Examples of external additives also include resin particles (resinparticles made of, for example, polystyrene, polymethyl methacrylate,and melamine resin), and cleaning active agents (e.g., higher fatty acidmetal salts, such as zinc stearate, fluoropolymer particles).

The amount of external additives externally added is preferably 0.01mass % or more and 5 mass % or less, more preferably 0.01 mass % or moreand 2.0 mass % or less relative to the total mass of thepressure-responsive particles (pressure-responsive base particles) otherthan the external additives.

Pressure Characteristics of Pressure-Responsive Particles

The pressure-responsive particles produced by the method for producingpressure-responsive particles according to the exemplary embodimentundergo pressure-induced phase transition and satisfy Formula 1 below.

10° C.≤T1−T2   Formula 1

In Formula 1, T1 is a temperature corresponding to a viscosity of 10,000Pas at a pressure of 1 MPa, and T2 is a temperature corresponding to aviscosity of 10,000 Pas at a pressure of 10 MPa.

The temperature difference (T1−T2) is 10 ° C. or more, preferably 15° C.or more, more preferably 20° C. or more in order to facilitate thepressure-induced phase transition of the pressure-responsive particles,and preferably 120° C. or less, more preferably 100° C. or less, stillmore preferably 80° C. or less in order to prevent fluidization of thepressure-responsive particles under no pressure.

The temperature T1 is preferably 140° C. or lower, more preferably 130°C. or lower, still more preferably 120° C. or lower, yet still morepreferably 115° C. or lower. The lower limit of the temperature T1 ispreferably 80° C. or higher, more preferably 85° C. or higher.

The temperature T2 is preferably 40° C. or higher, more preferably 50°C. or higher, still more preferably 60° C. or higher. The upper limit ofthe temperature T2 is preferably 85° C. or lower.

Examples of the indicator for the susceptibility of thepressure-responsive particles to pressure-induced phase transitioninclude a temperature difference (T1−T3) between the temperature T1corresponding to a viscosity of 10,000 Pas at a pressure of 1 MPa andthe temperature T3 corresponding to a viscosity of 10,000 Pas at apressure of 4 MPa. The temperature difference (T1−T3) may be 5° C. ormore. To facilitate the pressure-induced phase transition of thepressure-responsive particles, the temperature difference (T1−T3) ispreferably 5° C. or more, more preferably 10° C. or more.

The temperature difference (T1−T3) is typically 25° C. or less.

To obtain a temperature difference (T1−T3) of 5° C. or more, thetemperature T3 corresponding to a viscosity of 10,000 Pas at a pressureof 4 MPa for the pressure-responsive particles is preferably 90° C. orlower, more preferably 85° C. or lower, still more preferably 80° C. orlower. The lower limit of the temperature T3 is preferably 60° C. orhigher.

The method for determining the temperature T1, the temperature T2, andthe temperature T3 is as described below.

A pellet sample is prepared by compressing the pressure-responsiveparticles. The pellet sample is set in a flow tester (CFT-500 availablefrom Shimadzu Corporation). The applied pressure is fixed at 1 MPa, andthe viscosity against temperature at 1 MPa is measured. From theobtained viscosity graph, the temperature T1 corresponding to aviscosity of 10⁴ Pas at an applied pressure of 1 MPa is determined. Thetemperature T2 is determined in the same manner as that in the methodfor determining the temperature T1 except that the applied pressure ischanged from 1 MPa to 10 MPa. The temperature T3 is determined in thesame manner as that in the method for determining the temperature T1except that the applied pressure is changed from 1 MPa to 4 MPa. Thetemperature difference (T1−T2) is calculated from the temperature T1 andthe temperature T2. The temperature difference (T1−T3) is calculatedfrom the temperature T1 and the temperature T3.

Cartridge

A cartridge according to an exemplary embodiment storespressure-responsive particles produced by the method for producingpressure-responsive particles according to the exemplary embodiment andis attachable to or detachable from a printed material producingapparatus. When the cartridge is installed in a printed materialproducing apparatus, the cartridge is connected to a disposing unit ofthe printed material producing apparatus through a feed tube. Thedisposing unit disposes pressure-responsive particles on a recordingmedium.

The pressure-responsive particles are fed to the disposing unit from thecartridge. When the pressure-responsive particles stored in thecartridge runs short, the cartridge is replaced.

Printed Material Producing Apparatus, Method for Producing PrintedMaterial, Printed Material

The printed material producing apparatus according to the exemplaryembodiment includes: a disposing unit that stores pressure-sensitiveparticles produced by the method for producing pressure-responsiveparticles according to the exemplary embodiment and disposes thepressure-responsive particles on a recording medium; and apressure-bonding unit that folds the recording medium and pressure-bondsthe folded recording medium or stacks the recording medium and anotherrecording medium on top of each other and pressure-bonds the stackedrecording media to each other.

For example, the disposing unit may include an applying device thatapplies the pressure-responsive particles to a recording medium and mayfurther include a fixing device that fixes the pressure-responsiveparticles on the recording medium to the recording medium.

The pressure-bonding unit includes, for example, a folding device thatfolds the recording medium having the pressure-responsive particlesthereon or a stacking device that stacks the recording medium having thepressure-responsive particles thereon and another recording medium ontop of each other, and a pressure device that presses the foldedrecording medium or the stacked recording media.

The pressure device of the pressure-bonding unit applies pressure to therecording medium having the pressure-responsive particles thereon. Thepressure-responsive particles are thus fluidized on the recording mediumand exhibit adhesiveness.

The printed material producing apparatus according to the exemplaryembodiment executes a method for producing a printed material accordingto an exemplary embodiment. The method for producing a printed materialaccording to the exemplary embodiment includes: a disposing step ofdisposing, on a recording medium, pressure-responsive particles producedby the method for producing pressure-responsive particles according tothe exemplary embodiment; and a pressure-bonding step of folding therecording medium and pressure-bonding the folded recording medium, orstacking the recording medium and another recording medium on top ofeach other and pressure-bonding the stacked recording media to eachother.

For example, the disposing step may include a step of applying thepressure-responsive particles to a recording medium and may furtherinclude a step of fixing the pressure-responsive particles on therecording medium to the recording medium.

The pressure-bonding step includes, for example, a folding step offolding the recording medium or a stacking step of stacking therecording medium and another recording medium on top of each other, anda pressing step of pressing the folded recording medium or the stackedrecording media.

The pressure-responsive particles may be disposed on the entire surfaceof the recording medium or may be disposed on part of the recordingmedium. The pressure-responsive particles are disposed to form one layeror two or more layers on the recording medium. A layer of thepressure-responsive particles may be continuous in the plane directionof the recording medium or may be discontinuous in the plane directionof the recording medium. In a layer of the pressure-responsiveparticles, the pressure-responsive particles may be arranged in the formof particles, or may be arranged such that adjacent pressure-responsiveparticles fuse with each other.

The amount of the pressure-responsive particles (may be transparentpressure-responsive particles) on the recording medium in a region wherethe pressure-responsive particles are disposed is, for example, 0.5 g/m²or more and 50 g/m² or less, 1 g/m² or more and 40 g/m² or less, or 1.5g/m² or more and 30 g/m² or less. The layer thickness of thepressure-responsive particles (may be transparent pressure-responsiveparticles) on the recording medium is, for example, 0.2 μm or more and25 μm or less, 0.4 μm or more and 20 μm or less, or 0.6 μm or more and15 μm or less.

Examples of the recording medium used in the printed material producingapparatus according to the exemplary embodiment include paper, coatedpaper having the surface coated with resin or the like, fabrics,nonwoven fabrics, resin films, and resin sheets. The recording mediummay have an image on one side or both sides.

An example of the printed material producing apparatus according to theexemplary embodiment will be described below, but this exemplaryembodiment is not limited to this example.

FIG. 1 is a schematic structural view of one example of the printedmaterial producing apparatus according to the exemplary embodiment. Theprinted material producing apparatus shown in FIG. 1 includes adisposing unit 100 and a pressure-bonding unit 200 downstream of thedisposing unit 100. The arrows indicate the transport direction of arecording medium.

The disposing unit 100 is a device that disposes, on a recording mediumP, pressure-responsive particles produced by the method for producingpressure-responsive particles according to the exemplary embodiment. Animage is formed in advance on one side or both sides of the recordingmedium P.

The disposing unit 100 includes an applying device 110 and a fixingdevice 120 downstream of the applying device 110.

The applying device 110 applies pressure-responsive particles M to arecording medium P. Examples of the application method used in theapplying device 110 include spraying, bar coating, die coating, knifecoating, roll coating, reverse roll coating, gravure coating, screenprinting, an ink-jet method, lamination, and electrophotography.According to the application method, a liquid composition prepared bydispersing the pressure-responsive particles M in a dispersion mediummay be used in the applying device 110.

The recording medium P having the pressure-responsive particles Mapplied by the applying device 110 is transported to the fixing device120.

Examples of the fixing device 120 include a heating device that includesa heat source and heats the pressure-responsive particles M on arecording medium P passing through the device to fix thepressure-responsive particles M to the recording medium P; a pressuredevice that includes a pair of pressure members (roll/roll, belt/roll)and presses a recording medium P passing through the device to fix thepressure-responsive particles M to the recording medium P; and apressing and heating device that includes a pair of pressure members(roll/roll, belt/roll) having a heat source inside and presses and heatsa recording medium P passing through the device to fix thepressure-responsive particles M to the recording medium P.

When the fixing device 120 has a heat source, the surface temperature ofthe recording medium P heated by the fixing device 120 is preferably 10°C. or higher and 80° C. or lower, more preferably 20° C. or higher and60° C. or lower, still more preferably 30° C. or higher and 50° C. orlower.

When the fixing device 120 has pressure members, the pressure applied tothe recording medium P by the pressure members may be lower than thepressure applied to a recording medium P2 by a pressure device 230.

As the recording medium P passes through the disposing unit 100, therecording medium P becomes a recording medium P1 having thepressure-responsive particles M on an image. The recording medium P1 istransported toward the pressure-bonding unit 200.

In the printed material producing apparatus according to the exemplaryembodiment, the disposing unit 100 and the pressure-bonding unit 200 maybe adjacent to each other or may be distant from each other. When thedisposing unit 100 and the pressure-bonding unit 200 are distant fromeach other, the disposing unit 100 is connected to the pressure-bondingunit 200 through, for example, a transporting unit (e.g., a beltconveyor) that transports the recording medium P1.

The pressure-bonding unit 200 includes a folding device 220 and thepressure device 230 and folds the recording medium P1 and pressure-bondsthe folded recording medium P1.

The folding device 220 folds the recording medium P1 passing through thedevice to make a folded recording medium P2. The recording medium P2 is,for example, folded in two, three, or four. The recording medium P2 maybe partially folded. The pressure-responsive particles M are disposed onat least part of at least one of two opposing surfaces of the recordingmedium P2.

The folding device 220 may have a pair of pressure members (e.g.,roll/roll, belt/roll) that applies pressure to the recording medium P2.The pressure applied to the recording medium P2 by the pressure membersof the folding device 220 may be lower than the pressure applied to therecording medium P2 by the pressure device 230.

The pressure-bonding unit 200 may include, instead of the folding device220, a stacking device that stacks the recording medium P1 and anotherrecording medium on top of each other. The recording medium P1 andanother recording medium may be stacked on top of each other in such amanner that, for example, another recording medium is stacked on therecording medium P1 or other recording media are separately stacked ondifferent areas of the recording medium P1. Another recording medium oreach of other recording media may be a recording medium having an imageformed in advance on one side or both sides, a recording medium havingno image formed thereon, or a pressure-bonded printed material producedin advance.

The recording medium P2 discharged from the folding device 220 (or thestacking device) is transported toward the pressure device 230.

The pressure device 230 includes a pair of pressure members (i.e.,pressure rolls 231 and 232). The pressure roll 231 and the pressure roll232 are in contact with each other on their outer circumferentialsurfaces and press against each other to apply pressure to the recordingmedium P2 passing therebetween. A pair of pressure members in thepressure device 230 is not limited to a combination of a pressure rolland a pressure roll, and may be a combination of a pressure roll and apressure belt or a combination of a pressure belt and a pressure belt.

Upon application of pressure to the recording medium P2 passing throughthe pressure device 230, the pressure-responsive particles M arefluidized on the recording medium P2 under pressure and exhibitadhesiveness.

The pressure device 230 may or may not have, inside the device, a heatsource (e.g., a halogen heater) for heating the recording medium P2. Theabsence of a heat source in the pressure device 230 does not exclude thepossibility that heat generation from a motor or the like in thepressure device 230 increases the temperature in the pressure device 230to an environmental temperature or higher.

When the recording medium P2 passes through the pressure device 230, theopposing surfaces of the folded recording medium P2 are bonded to eachother with the fluidized pressure-responsive particles M to produce apressure-bonded printed material P3. Two opposing surfaces of thepressure-bonded printed material P3 are partially or entirely bonded toeach other.

The completed pressure-bonded printed material P3 is discharged from thepressure device 230.

A first form of the pressure-bonded printed material P3 is apressure-bonded printed material formed by bonding the opposing surfacesof a folded recording medium to each other with the pressure-responsiveparticles M. The pressure-bonded printed material P3 in this form isproduced by a printed material producing apparatus including the foldingdevice 220.

A second form of the pressure-bonded printed material P3 is apressure-bonded printed material formed by bonding the opposing surfacesof stacked recording media to each other with the pressure-responsiveparticles M. The pressure-bonded printed material P3 in this form isproduced by a pressure-bonded printed material producing apparatusincluding a stacking device.

The printed material producing apparatus according to the exemplaryembodiment is not limited to an apparatus in which the recording mediaP2 are continuously transported from the folding device 220 (or thestacking device) to the pressure device 230. The printed materialproducing apparatus according to the exemplary embodiment may be anapparatus in which recording media P2 discharged from the folding device220 (or the stacking device) are stored and, after the storage ofrecording media P2 reaches a predetermined amount, the recording mediaP2 are transported to the pressure device 230.

In the printed material producing apparatus according to the exemplaryembodiment, the folding device 220 (or the stacking device) and thepressure device 230 may be adjacent to each other or may be distant fromeach other. When the folding device 220 (or the stacking device) and thepressure device 230 are distant from each other, the folding device 220(or the stacking device) is connected to the pressure device 230through, for example, a transporting unit (e.g., a belt conveyor) thattransports the recording medium P2.

The printed material producing apparatus according to the exemplaryembodiment may include a cutting unit that cuts a recording medium intoa predetermined size. Examples of the cutting unit include a cuttingunit that is disposed between the disposing unit 100 and thepressure-bonding unit 200 and cuts away a region that is part of therecording medium P1 and that has no pressure-responsive particles Mthereon; a cutting unit that is disposed between the folding device 220and the pressure device 230 and cuts away a region that is part of therecording medium P2 and that has no pressure-responsive particles Mthereon; and a cutting unit that is disposed downstream of thepressure-bonding unit 200 and cuts away a region that is part of thepressure-bonded printed material P3 and that is not bonded with thepressure-responsive particles M.

The printed material producing apparatus according to the exemplaryembodiment is not limited to a sheet-fed apparatus. The printed materialproducing apparatus according to the exemplary embodiment may be anapparatus that forms a long pressure-bonded printed material bysubjecting a long recording medium to the disposing step and thepressure-bonding step, and then cuts the long pressure-bonded printedmaterial into a predetermined size.

The printed material producing apparatus according to the exemplaryembodiment may further include a color image forming unit that forms acolor image on a recording medium by using a color material. Examples ofthe color image forming unit include a unit that forms a color ink imageon a recording medium by an ink-jet system using color ink as a colormaterial, and a unit that forms a color image on a recording medium byan electrophotographic system using a color electrostatic charge imagedeveloper.

The producing apparatus having the above structure executes the methodfor producing a printed material according to the exemplary embodimentfurther including a color image forming step of forming a color image ona recording medium by using a color material. Examples of the colorimage forming step include a step of forming a color ink image on arecording medium by an ink-jet system using color ink as a colormaterial, and a step of forming a color image on a recording medium byan electrophotographic system using a color electrostatic charge imagedeveloper.

Sheet for Producing Printed Material and Method for Producing Sheet forProducing Printed Material

A sheet for producing a printed material according to an exemplaryembodiment includes a substrate and pressure-responsive particlesdisposed on the substrate. The sheet for producing a printed materialaccording to the exemplary embodiment is produced by usingpressure-responsive particles produced by the method for producingpressure-responsive particles according to the exemplary embodiment. Thepressure-responsive particles on the substrate may or may not keep thesame particle shape as before being disposed on the substrate.

The sheet for producing a printed material according to the exemplaryembodiment is used as, for example, a masking sheet to be stacked on andbonded to a recording medium in order to conceal information recorded onthe recording medium; or as a release sheet used to provide an adhesivelayer on a recording medium when recording media are stacked and bondedto each other.

Examples of the substrate used in the sheet for producing a printedmaterial according to the exemplary embodiment include paper, coatedpaper having the surface coated with resin or the like, fabrics,nonwoven fabrics, resin films, and resin sheets. The substrate may havean image formed on one side or both sides.

In the sheet for producing a printed material according to the exemplaryembodiment, the pressure-responsive particles may be disposed on theentire surface of the substrate or may be disposed on part of thesubstrate. The pressure-responsive particles are disposed to form onelayer or two or more layers on the substrate. A layer of thepressure-responsive particles may be continuous in the plane directionof the substrate or may be discontinuous in the plane direction of thesubstrate. In a layer of the pressure-responsive particles, thepressure-responsive particles may be arranged in the form of particles,or may be arranged such that adjacent pressure-responsive particles fusewith each other.

The amount of the pressure-responsive particles on the substrate in aregion where the pressure-responsive particles are disposed is, forexample, 0.5 g/m² or more and 50 g/m² or less, 1 g/m² or more and 40g/m² or less, or 1.5 g/m² or more and 30 g/m² or less. The layerthickness of the pressure-responsive particles on the substrate is, forexample, 0.2 μm or more and 25 μm or less, 0.4 μm or more and 20 μm orless, or 0.6 μm or more and 15 μm or less.

The sheet for producing a printed material according to the exemplaryembodiment is produced by, for example, a production method including adisposing step of disposing, on the substrate, pressure-responsiveparticles produced by the method for producing pressure-responsiveparticles according to the exemplary embodiment.

For example, the disposing step may include an applying step of applyingthe pressure-responsive particles to the substrate and may furtherinclude a fixing step of fixing the pressure-responsive particles on thesubstrate to the substrate.

The applying step is achieved by an application method, such asspraying, bar coating, die coating, knife coating, roll coating, reverseroll coating, gravure coating, screen printing, an ink-jet method,lamination, or electrophotography. According to the application methodin the applying step, a liquid composition prepared by dispersing thepressure-responsive particles in a dispersion medium may be used in theapplying step.

Examples of the fixing step include a heating step of heating thepressure-responsive particles on the substrate to fix thepressure-responsive particles to the substrate; a pressing step ofpressing the substrate having the pressure-responsive particles appliedthereon with a pair of pressure members (roll/roll, belt/roll) to fixthe pressure-responsive particles to the substrate; and a pressing andheating step of pressing and heating the substrate having thepressure-responsive particles applied thereon with a pair of pressuremembers (roll/roll, belt/roll) having a heat source inside to fix thepressure-responsive particles to the substrate.

Production of Printed Material by Electrophotographic System

An exemplary embodiment of application of the pressure-responsiveparticles produced by the method for producing pressure-responsiveparticles according to the exemplary embodiment to anelectrophotographic system will be described. In the electrophotographicsystem, the pressure-responsive particles may be used as toner.

Electrostatic Charge Image Developer

An electrostatic charge image developer according to an exemplaryembodiment contains at least pressure-responsive particles produced bythe method for producing pressure-responsive particles according to theexemplary embodiment. The electrostatic charge image developer accordingto the exemplary embodiment may be a one-component developer containingonly the pressure-responsive particles, or may be a two-componentdeveloper containing a mixture of the pressure-responsive particles anda carrier.

The carrier is not limited, and may be a known carrier. Examples of thecarrier include a coated carrier obtained by coating, with resin, thesurface of a core made of magnetic powder; a magnetic powder-dispersedcarrier in which magnetic powder is dispersed and mixed in matrix resin;and a resin-impregnated carrier in which porous magnetic powder isimpregnated with resin. The magnetic powder-dispersed carrier or theresin-impregnated carrier may be a carrier having constituent particlesas a core and a resin coating the surfaces of the constituent particles.

Examples of the magnetic powder include powders made of magnetic metals,such as iron, nickel, and cobalt; and powders made of magnetic oxides,such as ferrite and magnetite.

Examples of the coating resin and the matrix resin include polyethylene,polypropylene, polystyrene, polyvinyl acetate, polyvinyl alcohol,polyvinyl butyral, polyvinyl chloride, polyvinyl ether, polyvinylketone, a vinyl chloride-vinyl acetate copolymer, a styrene-acrylic acidester copolymer, a straight silicone resin including an organosiloxanebond, and modified products thereof, fluorocarbon resin, polyester,polycarbonate, phenolic resin, and epoxy resin. The coating resin andthe matrix resin may contain other additives, such as conductiveparticles. Examples of the conductive particles include particles madeof metals, such as gold, silver, and copper; and particles made ofcarbon black, titanium oxide, zinc oxide, tin oxide, barium sulfate,aluminum borate, and potassium titanate.

The surface of the core is coated with resin by, for example, a coatingmethod using a coating layer-forming solution in which a coating resinand various additives (used as desired) are dissolved in an appropriatesolvent. The solvent is not limited and may be selected in considerationof the type of resin used, coating suitability, and the like.

Specific examples of the resin coating method include an immersionmethod that involves immersing the core in the coating layer-formingsolution; a spray method that involves spraying the coatinglayer-forming solution onto the surface of the core; a fluidized bedmethod that involves spraying the coating layer-forming solution ontothe core while floating the core in air flow; and a kneader-coatermethod that involves mixing the core of the carrier and the coatinglayer-forming solution in a kneader-coater, and then removing thesolvent.

The mixing ratio (mass ratio) of the pressure-responsive particles tothe carrier in the two-component developer is preferably from 1:100 to30:100(=pressure-responsive particles:carrier), more preferably from3:100 to 20:100.

Printed Material Producing Apparatus, Method for Producing PrintedMaterial

A printed material producing apparatus using an electrophotographicsystem includes: a disposing unit that stores a developer containingpressure-responsive particles produced by the method for producingpressure-responsive particles according to the exemplary embodiment anddisposes the pressure-responsive particles on a recording medium byusing the electrophotographic system; and a pressure-bonding unit thatfolds the recording medium and pressure-bonds the folded recordingmedium or stacks the recording medium and another recording medium ontop of each other and pressure-bonds the stacked recording media to eachother.

The printed material producing apparatus according to the exemplaryembodiment executes a method for producing a printed material using anelectrophotographic system. The method for producing a printed materialaccording to the exemplary embodiment includes: a disposing step ofdisposing pressure-responsive particles on a recording medium by anelectrophotographic system using a developer containing thepressure-responsive particles, the pressure-responsive particles beingproduced by the method for producing pressure-responsive particlesaccording to the exemplary embodiment; and a pressure-bonding step offolding the recording medium and pressure-bonding the folded recordingmedium, or stacking the recording medium and another recording medium ontop of each other and pressure-bonding the stacked recording media toeach other.

The disposing unit in the printed material producing apparatus accordingto the exemplary embodiment includes: for example,

a photoreceptor;

a charging unit that charges the surface of the photoreceptor;

an electrostatic charge image forming unit that forms an electrostaticcharge image on the charged surface of the photoreceptor;

a developing unit that stores the electrostatic charge image developeraccording to the exemplary embodiment and develops the electrostaticcharge image on the surface of the photoreceptor by using theelectrostatic charge image developer to form a pressure-responsiveparticle-applied section; and

a transfer unit that transfers the pressure-responsive particle-appliedsection on the surface of the photoreceptor to the surface of arecording medium.

The disposing unit may further include a fixing unit that fixes thepressure-responsive particle-applied section which has been transferredto the surface of the recording medium.

The disposing step in the method for producing a printed materialaccording to the exemplary embodiment includes: for example,

a charging step of charging the surface of the photoreceptor;

an electrostatic charge image forming step of forming an electrostaticcharge image on the charged surface of the photoreceptor;

a developing step of developing the electrostatic charge image on thesurface of the photoreceptor by using the electrostatic charge imagedeveloper according to the exemplary embodiment to form apressure-responsive particle-applied section; and

a transferring step of transferring the pressure-responsiveparticle-applied section on the surface of the photoreceptor to thesurface of a recording medium.

The disposing step may further include a fixing step of fixing thepressure-responsive particle-applied section which has been transferredto the surface of the recording medium.

Examples of the disposing unit include devices, such as a directtransfer-type device in which a pressure-responsive particle-appliedsection formed on the surface of a photoreceptor is directly transferredto a recording medium; an intermediate transfer-type device in which apressure-responsive particle-applied section formed on the surface of aphotoreceptor is first transferred to the surface of an intermediatetransfer body, and the pressure-responsive particle-applied section,which has been transferred to the surface of the intermediate transferbody, is second transferred to the surface of a recording medium; adevice including a cleaning unit that cleans the surface of aphotoreceptor before charging after transfer of the pressure-responsiveparticle-applied section; and a device including a discharging unit thatdischarges the surface of a photoreceptor by irradiating the surface ofthe photoreceptor with discharging light before charging after transferof a pressure-responsive particle-applied section. When the disposingunit is an intermediate transfer-type device, the transfer unitincludes, for example, an intermediate transfer body having the surfaceto which a pressure-responsive particle-applied section is transferred,a first transfer unit that first transfers the pressure-responsiveparticle-applied section on the surface of the photoreceptor to thesurface of the intermediate transfer body, and a second transfer unitthat second transfers the pressure-responsive particle-applied section,which has been transferred to the surface of the intermediate transferbody, to the surface of a recording medium.

In the disposing unit, a section including the developing unit may havea cartridge structure (i.e., process cartridge) that is attachable toand detachable from the disposing unit. The process cartridge may be,for example, a process cartridge that stores the electrostatic chargeimage developer according to the exemplary embodiment and that includesthe developing unit.

The pressure-bonding unit in the printed material producing apparatusaccording to the exemplary embodiment applies pressure to a recordingmedium having thereon pressure-responsive particles produced by themethod for producing pressure-responsive particles according to theexemplary embodiment. The pressure-responsive particles are thusfluidized on the recording medium and exhibit adhesiveness. The pressureapplied to the recording medium by the pressure-bonding unit in order tofluidize the pressure-responsive particles is preferably 3 MPa or moreand 300 MPa or less, more preferably 10 MPa or more and 200 MPa or less,still more preferably 30 MPa or more and 150 MPa or less.

The pressure-responsive particles may be disposed on the entire surfaceof the recording medium or may be disposed on part of the recordingmedium. The pressure-responsive particles are disposed to form one layeror two or more layers on the recording medium. A layer of thepressure-responsive particles may be continuous in the plane directionof the recording medium or may be discontinuous in the plane directionof the recording medium. In a layer of the pressure-responsiveparticles, the pressure-responsive particles may be arranged in the formof particles, or may be arranged such that adjacent pressure-responsiveparticles fuse with each other.

The amount of the pressure-responsive particles (may be transparentpressure-responsive particles) on the recording medium in a region wherethe pressure-responsive particles are disposed is, for example, 0.5 g/m²or more and 50 g/m² or less, 1 g/m² or more and 40 g/m² or less, or 1.5g/m² or more and 30 g/m² or less. The layer thickness of thepressure-responsive particles (may be transparent pressure-responsiveparticles) on the recording medium is, for example, 0.2 μm or more and25 μm or less, 0.4 μm or more and 20 μm or less, or 0.6 μm or more and15 μm or less.

Examples of the recording medium used in the printed material producingapparatus according to the exemplary embodiment include paper, coatedpaper having the surface coated with resin or the like, fabrics,nonwoven fabrics, resin films, and resin sheets. The recording mediummay have an image on one side or both sides.

An example of the printed material producing apparatus according to theexemplary embodiment using an electrophotographic system will bedescribed below, but this exemplary embodiment is not limited to thisexample.

FIG. 2 is a schematic structural view of one example of the printedmaterial producing apparatus according to the exemplary embodiment. Theprinted material producing apparatus shown in FIG. 2 includes adisposing unit 100 and a pressure-bonding unit 200 downstream of thedisposing unit 100. The arrows indicate the rotation direction of aphotoreceptor or the transport direction of a recording medium.

The disposing unit 100 is a direct transfer-type device that disposes,on a recording medium P, pressure-responsive particles produced by themethod for producing pressure-responsive particles according to theexemplary embodiment by an electrophotographic system using a developercontaining the pressure-responsive particles produced by the method forproducing pressure-responsive particles according to the exemplaryembodiment. An image is formed in advance on one side or both sides ofthe recording medium P.

The disposing unit 100 has a photoreceptor 101. The photoreceptor 101 issurrounded by, in sequence, a charging roll (an example of the chargingunit) 102, which charges the surface of the photoreceptor 101, anexposure device (an example of the electrostatic charge image formingunit) 103, which exposes the charged surface of the photoreceptor 101 toa laser beam to form an electrostatic charge image, a developing device(an example of the developing unit) 104, which suppliespressure-responsive particles to the electrostatic charge image todevelop the electrostatic charge image, a transfer roll (an example ofthe first transfer unit) 105, which transfers the developedpressure-responsive particle-applied section to a recording medium P,and a photoreceptor cleaning device (an example of the cleaning unit)106, which removes the pressure-responsive particles remaining on thesurface of the photoreceptor 101 after the transfer.

The operation of the disposing unit 100 for disposing, on a recordingmedium P, pressure-responsive particles produced by the method forproducing pressure-responsive particles according to the exemplaryembodiment will be described.

First, the charging roll 102 charges the surface of the photoreceptor101. The charged surface of the photoreceptor 101 is irradiated with alaser beam from the exposure device 103 in accordance with image datasent from a controller (not shown). An electrostatic charge image havinga pattern of the pressure-responsive particles is accordingly formed onthe surface of the photoreceptor 101.

The electrostatic charge image formed on the photoreceptor 101 rotatesto a development position as the photoreceptor 101 runs. At thedevelopment position, the electrostatic charge image on thephotoreceptor 101 is developed by the developing device 104 to form apressure-responsive particle-applied section.

The developing device 104 stores a developer containing at least thepressure-responsive particles and a carrier. The pressure-responsiveparticles are triboelectrically charged by stirring thepressure-responsive particles together with the carrier inside thedeveloping device 104 and held on a developer roll. As the surface ofthe photoreceptor 101 passes through the developing device 104, thepressure-responsive particles electrostatically adhere to theelectrostatic charge image on the surface of the photoreceptor 101,whereby the electrostatic charge image is developed with thepressure-responsive particles. The photoreceptor 101 having thepressure-responsive particle-applied section thereon subsequently runs,and the pressure-responsive particle-applied section on thephotoreceptor 101 is transported to a transfer position.

Upon the pressure-responsive particle-applied section on thephotoreceptor 101 reaching the transfer position, a transfer bias isapplied to the transfer roll 105 so that an electrostatic force from thephotoreceptor 101 toward the transfer roll 105 acts on thepressure-responsive particle-applied section, transferring thepressure-responsive particle-applied section on the photoreceptor 101 tothe recording medium P.

The pressure-responsive particles remaining on the photoreceptor 101 areremoved and collected by the photoreceptor cleaning device 106. Thephotoreceptor cleaning device 106 is, for example, a cleaning blade or acleaning brush. The photoreceptor cleaning device 106 may be a cleaningbrush in order to prevent a phenomenon in which the pressure-responsiveparticles remaining on the surface of the photoreceptor are fluidizedunder pressure and adhere to the surface of the photoreceptor to form alayer.

The recording medium P to which the pressure-responsive particle-appliedsection has been transferred is transported to a fixing device (anexample of the fixing unit) 107. The fixing device 107 is, for example,a pair of fixing members (e.g., roll/roll, belt/roll). The disposingunit 100 may not include the fixing device 107 but may include thefixing device 107 in order to prevent the pressure-responsive particlesfrom falling off the recording medium P. The pressure applied to therecording medium P by the fixing device 107 may be lower than thepressure applied to a recording medium P2 by a pressure device 230.Specifically, the pressure may be 0.2 MPa or more and 1 MPa or less.

The fixing device 107 may or may not have, inside the device, a heatsource (e.g., a halogen heater) for heating the recording medium P. Whenthe fixing device 107 has a heat source inside, the surface temperatureof the recording medium P heated by the heat source is preferably 150°C. or higher and 220° C. or lower, more preferably 155° C. or higher and210° C. or lower, still more preferably 160° C. or higher and 200° C. orlower. The absence of a heat source in the fixing device 107 does notexclude the possibility that heat generation from a motor or the like inthe disposing unit 100 increases the temperature in the fixing device107 to an environmental temperature or higher.

As the recording medium P passes through the disposing unit 100, therecording medium P becomes a recording medium P1 having thepressure-responsive particles on an image. The recording medium P1 istransported toward the pressure-bonding unit 200.

In the printed material producing apparatus according to the exemplaryembodiment, the disposing unit 100 and the pressure-bonding unit 200 maybe adjacent to each other or may be distant from each other. When thedisposing unit 100 and the pressure-bonding unit 200 are distant fromeach other, the disposing unit 100 is connected to the pressure-bondingunit 200 through, for example, a transporting unit (e.g., a beltconveyor) that transports the recording medium P1.

The pressure-bonding unit 200 includes a folding device 220 and thepressure device 230 and folds the recording medium P1 and pressure-bondsthe folded recording medium P1.

The folding device 220 folds the recording medium P1 passing through thedevice to make a folded recording medium P2. The recording medium P2 is,for example, folded in two, three, or four. The recording medium P2 maybe partially folded. The pressure-responsive particles are disposed onat least part of at least one of two opposing surfaces of the recordingmedium P2.

The folding device 220 may have a pair of pressure members (e.g.,roll/roll, belt/roll) that applies pressure to the recording medium P2.The pressure applied to the recording medium P2 by the pressure membersof the folding device 220 may be lower than the pressure applied to therecording medium P2 by the pressure device 230. Specifically, thepressure may be 1 MPa or more and 10 MPa or less.

The pressure-bonding unit 200 may include, instead of the folding device220, a stacking device that stacks the recording medium P1 and anotherrecording medium on top of each other. The recording medium P1 andanother recording medium may be stacked on top of each other in such amanner that, for example, another recording medium is stacked on therecording medium P1 or other recording media are separately stacked ondifferent areas of the recording medium P1. Another recording medium oreach of other recording media may be a recording medium having an imageformed in advance on one side or both sides, a recording medium havingno image formed thereon, or a pressure-bonded printed material producedin advance.

The recording medium P2 discharged from the folding device 220 (or thestacking device) is transported toward the pressure device 230.

The pressure device 230 includes a pair of pressure members (i.e.,pressure rolls 231 and 232). The pressure roll 231 and the pressure roll232 are in contact with each other on their outer circumferentialsurfaces and press against each other to apply pressure to the recordingmedium P2 passing therebetween. A pair of pressure members in thepressure device 230 is not limited to a combination of a pressure rolland a pressure roll, and may be a combination of a pressure roll and apressure belt or a combination of a pressure belt and a pressure belt.

Upon application of pressure to the recording medium P2 passing throughthe pressure device 230, the pressure-responsive particles are fluidizedon the recording medium P2 under pressure and exhibit adhesiveness. Thepressure applied to the recording medium P2 by the pressure device 230is preferably 3 MPa or more and 300 MPa or less, more preferably 10 MPaor more and 200 MPa or less, still more preferably 30 MPa or more and150 MPa or less.

The pressure device 230 may or may not have, inside the device, a heatsource (e.g., a halogen heater) for heating the recording medium P2.When the pressure device 230 has a heat source inside, the surfacetemperature of the recording medium P2 heated by the heat source ispreferably 30° C. or higher and 120° C. or lower, more preferably 40° C.or higher and 100° C. or lower, still more preferably 50° C. or higherand 90° C. or lower. The absence of a heat source in the pressure device230 does not exclude the possibility that heat generation from a motoror the like in the pressure device 230 increases the temperature in thepressure device 230 to an environmental temperature or higher.

When the recording medium P2 passes through the pressure device 230, theopposing surfaces of the folded recording medium P2 are bonded to eachother with the fluidized pressure-responsive particles to produce apressure-bonded printed material P3. The opposing surfaces of thepressure-bonded printed material P3 are partially or entirely bonded toeach other.

The completed pressure-bonded printed material P3 is discharged from thepressure device 230.

A first form of the pressure-bonded printed material P3 is apressure-bonded printed material formed by bonding the opposing surfacesof a folded recording medium to each other with the pressure-responsiveparticles. The pressure-bonded printed material P3 in this form isproduced by a printed material producing apparatus including the foldingdevice 220.

A second form of the pressure-bonded printed material P3 is apressure-bonded printed material formed by bonding the opposing surfacesof stacked recording media to each other with pressure-responsiveparticles produced by the method for producing pressure-responsiveparticles according to the exemplary embodiment. The pressure-bondedprinted material P3 in this form is produced by a pressure-bondedprinted material producing apparatus including a stacking device.

The printed material producing apparatus according to the exemplaryembodiment is not limited to an apparatus in which the recording mediaP2 are continuously transported from the folding device 220 (or thestacking device) to the pressure device 230. The printed materialproducing apparatus according to the exemplary embodiment may be anapparatus in which recording media P2 discharged from the folding device220 (or the stacking device) are stored and, after the storage ofrecording media P2 reaches a predetermined amount, the recording mediaP2 are transported to the pressure device 230.

In the printed material producing apparatus according to the exemplaryembodiment, the folding device 220 (or the stacking device) and thepressure device 230 may be adjacent to each other or may be distant fromeach other. When the folding device 220 (or the stacking device) and thepressure device 230 are distant from each other, the folding device 20(or the stacking device) is connected to the pressure device 230through, for example, a transporting unit (e.g., a belt conveyor) thattransports the recording medium P2.

The printed material producing apparatus according to the exemplaryembodiment may include a cutting unit that cuts a recording medium intoa predetermined size. Examples of the cutting unit include a cuttingunit that is disposed between the disposing unit 100 and thepressure-bonding unit 200 and cuts away a region that is part of therecording medium P1 and that does not have thereon pressure-responsiveparticles produced by the method for producing pressure-responsiveparticles according to the exemplary embodiment; a cutting unit that isdisposed between the folding device 220 and the pressure device 230 andcuts away a region that is part of the recording medium P2 and that doesnot have the pressure-responsive particles thereon; and a cutting unitthat is disposed downstream of the pressure-bonding unit 200 and cutsaway a region that is part of the pressure-bonded printed material P3and that is not bonded with the pressure-responsive particles accordingto the exemplary embodiment.

The printed material producing apparatus according to the exemplaryembodiment is not limited to a sheet-fed apparatus. The printed materialproducing apparatus according to the exemplary embodiment may be anapparatus that forms a long pressure-bonded printed material bysubjecting a long recording medium to the disposing step and thepressure-bonding step, and then cuts the long pressure-bonded printedmaterial into a predetermined size.

The printed material producing apparatus according to the exemplaryembodiment may further include a color image forming unit that forms acolor image on a recording medium by an electrophotographic system usinga color electrostatic charge image developer. The color image formingunit includes: for example,

a photoreceptor;

a charging unit that charges the surface of the photoreceptor;

an electrostatic charge image forming unit that forms an electrostaticcharge image on the charged surface of the photoreceptor;

a developing unit that stores a color electrostatic charge imagedeveloper and develops the electrostatic charge image on the surface ofthe photoreceptor by using the color electrostatic charge imagedeveloper to form a color toner image;

a transfer unit that transfers the color toner image on the surface ofthe photoreceptor to the surface of a recording medium; and

a thermal fixing unit that thermally fixes the color toner image whichhas been transferred to the surface of the recording medium.

The producing apparatus having the above structure executes the methodfor producing a printed material according to the exemplary embodimentfurther including a color image forming step of forming a color image ona recording medium by an electrophotographic system using a colorelectrostatic charge image developer. Specifically, the color imageforming step includes:

a charging step of charging the surface of the photoreceptor;

an electrostatic charge image forming step of forming an electrostaticcharge image on the charged surface of the photoreceptor;

a developing step of developing the electrostatic charge image on thesurface of the photoreceptor by using a color electrostatic charge imagedeveloper to form a color toner image;

a transferring step of transferring the color toner image on the surfaceof the photoreceptor to the surface of a recording medium; and

a thermal fixing step of thermally fixing the color toner image whichhas been transferred to the surface of the recording medium.

Examples of the color image forming unit in the printed materialproducing apparatus according to the exemplary embodiment includedevices, such as a direct transfer-type device in which a color tonerimage formed on the surface of a photoreceptor is directly transferredto a recording medium; an intermediate transfer-type device in which acolor toner image formed on the surface of a photoreceptor is firsttransferred to the surface of an intermediate transfer body, and thecolor toner image, which has been transferred to the surface of theintermediate transfer body, is second transferred to the surface of arecording medium; a device including a cleaning unit that cleans thesurface of a photoreceptor before charging after transfer of a colortoner image; and a device including a discharging unit that dischargesthe surface of a photoreceptor by irradiating the surface of thephotoreceptor with discharging light before charging after transfer of acolor toner image. When the color image forming unit is an intermediatetransfer-type device, the transfer unit includes, for example, anintermediate transfer body having the surface to which a color tonerimage is transferred, a first transfer unit that first transfers thecolor toner image on the surface of the photoreceptor to the surface ofthe intermediate transfer body, and a second transfer unit that secondtransfers the color toner image, which has been transferred to thesurface of the intermediate transfer body, to the surface of a recordingmedium.

When the color image forming unit and the disposing unit for a developercontaining pressure-responsive particles produced by the method forproducing pressure-responsive particles according to the exemplaryembodiment are intermediate transfer-type devices in the printedmaterial producing apparatus according to the exemplary embodiment, thedisposing unit and the color image forming unit may share theintermediate transfer body and the second transfer unit.

In the printed material producing apparatus according to the exemplaryembodiment, the color image forming unit and the disposing unit for adeveloper containing the pressure-responsive particles produced by themethod for producing pressure-responsive particles according to theexemplary embodiment may share the thermal fixing unit.

An example of the printed material producing apparatus according to theexemplary embodiment including the color image forming unit will bedescribed below, but the exemplary embodiment is not limited to thisexample. The main parts shown in the figure will be described below, andother parts will not be described.

FIG. 3 is a schematic structural view of one example of the printedmaterial producing apparatus according to the exemplary embodiment usingan electrophotographic system. The printed material producing apparatusshown in FIG. 3 includes a printing unit 300 and a pressure-bonding unit200 downstream of the printing unit 300. The printing unit 300 disposes,on a recording medium, pressure-responsive particles produced by themethod for producing pressure-responsive particles according to theexemplary embodiment and forms color images in one process.

The printing unit 300 is of intermediate transfer type using a fivecolor tandem system. The printing unit 300 includes a unit 10T and units10Y, 10M, 10C, and 10K. The unit 10T disposes the pressure-responsiveparticles (T). The units 10Y, 10M, 10C, and 10K respectively form colorimages of yellow (Y), magenta (M), cyan (C), and black (K). The unit 10Tis a disposing unit that disposes the pressure-responsive particles on arecording medium P by using a developer containing thepressure-responsive particles. The units 10Y, 10M, 10C, and 10K eachform a color image on the recording medium P by using a developercontaining a color toner. The units 10T, 10Y, 10M, 10C, and 10K each usean electrophotographic system.

The units 10T, 10Y, 10M, 10C, and 10K are arranged and spaced apart fromeach other in the horizontal direction. The units 10T, 10Y, 10M, 10C,and 10K may be process cartridges that are attachable to and detachablefrom the printing unit 300.

An intermediate transfer belt (an example of the intermediate transferbody) 20 extends so as to pass through lower parts of the units 10T,10Y, 10M, 10C, and 10K. The intermediate transfer belt 20 is woundaround a drive roll 22, a support roll 23, and an opposing roll 24,which are in contact with the inner surface of the intermediate transferbelt 20. The intermediate transfer belt 20 runs in the direction fromthe unit 10T toward the unit 10K. An intermediate transfer body cleaningdevice 21 is disposed adjacent to the image holding surface of theintermediate transfer belt 20 so as to face the drive roll 22.

The units 10T, 10Y, 10M, 10C, and 10K respectively include developingdevices (examples of the developing units) 4T, 4Y, 4M, 4C, and 4K. Thepressure-responsive particles stored in a pressure-responsive particlecartridge 8T and yellow toner, magenta toner, cyan toner, and blacktoner respectively stored in toner cartridges 8Y, 8M, 8C, and 8K arerespectively supplied to the developing devices 4T, 4Y, 4M, 4C, and 4K.

Since the units 10T, 10Y, 10M, 10C, and 10K have the same structure andthe same operation, the unit 10T which disposes the pressure-responsiveparticles on a recording medium will be described as a representativeexample.

The unit 10T has a photoreceptor 1T. The photoreceptor 1T is surroundedby, in sequence, a charging roll (an example of the charging unit) 2T,which charges the surface of the photoreceptor 1T, an exposure device(an example of the electrostatic charge image forming unit) 3T, whichexposes the charged surface of the photoreceptor 1T to a laser beam toform an electrostatic charge image, a developing device (an example ofthe developing unit) 4T, which supplies pressure-responsive particles tothe electrostatic charge image to develop the electrostatic chargeimage, a first transfer roll (an example of the first transfer unit) 5T,which transfers the developed pressure-responsive particle-appliedsection to an intermediate transfer belt 20, and a photoreceptorcleaning device (an example of the cleaning unit) 6T, which removes thepressure-responsive particles remaining on the surface of thephotoreceptor 1T after the first transfer. The first transfer roll 5T isdisposed on the inner side of the intermediate transfer belt 20 so as toface the photoreceptor 1T.

The operation for disposing, on the recording medium P,pressure-responsive particles produced by the method for producingpressure-responsive particles according to the exemplary embodiment andthe operation for forming color images will be described below byillustrating the operation of the unit 10T.

First, the charging roll 2T charges the surface of the photoreceptor 1T.The charged surface of the photoreceptor 1T is irradiated with a laserbeam from the exposure device 3T in accordance with image data sent froma controller (not shown). An electrostatic charge image having a patternof the pressure-responsive particles is accordingly formed on thesurface of the photoreceptor 1T.

The electrostatic charge image formed on the photoreceptor 1T rotates toa development position as the photoreceptor 1T runs. At the developmentposition, the electrostatic charge image on the photoreceptor 1T isdeveloped by the developing device 4T to form a pressure-responsiveparticle-applied section.

The developing device 4T stores a developer containing at least thepressure-responsive particles and a carrier. The pressure-responsiveparticles are triboelectrically charged by stirring thepressure-responsive particles together with the carrier inside thedeveloping device 4T and held on a developer roll. As the surface of thephotoreceptor 1T passes through the developing device 4T, thepressure-responsive particles electrostatically adhere to theelectrostatic charge image on the surface of the photoreceptor 1T,whereby the electrostatic charge image is developed with thepressure-responsive particles. The photoreceptor 1T having thepressure-responsive particle-applied section thereon subsequently runs,and the pressure-responsive particle-applied section on thephotoreceptor 1T is transported to a first transfer position.

Upon the pressure-responsive particle-applied section on thephotoreceptor 1T reaching the first transfer position, a first transferbias is applied to the first transfer roll 5T so that an electrostaticforce from the photoreceptor 1T toward the first transfer roll 5T actson the pressure-responsive particle-applied section, transferring thepressure-responsive particle-applied section on the photoreceptor 1T tothe intermediate transfer belt 20. The pressure-responsive particlesremaining on the photoreceptor 1T are removed and collected by thephotoreceptor cleaning device 6T. The photoreceptor cleaning device 6Tis, for example, a cleaning blade or a cleaning brush, preferably acleaning brush.

The units 10Y, 10M, 10C, and 10K also operate in the same manner as theunit 10T by using developers containing color toner. Accordingly, theintermediate transfer belt 20 to which the pressure-responsiveparticle-applied section has been transferred in the unit 10T passesthrough the units 10Y, 10M, 10C, and 10K in this order, and the tonerimages of respective colors are transferred to the intermediate transferbelt 20 in a superimposed manner.

The intermediate transfer belt 20 to which the pressure-responsiveparticle-applied section and the toner images have been transferredthrough the units 10T, 10Y, 10M, 10C, and 10K in a superimposed mannerreaches a second transfer section. The second transfer section includesthe intermediate transfer belt 20, the opposing roll 24 in contact withthe inner surface of the intermediate transfer belt, and a secondtransfer roll (an example of the second transfer unit) 26 disposedadjacent to the image holding surface of the intermediate transfer belt20. The recording medium P is fed to a nip between the second transferroll 26 and the intermediate transfer belt 20 by way of a feedingmechanism, and a second transfer bias is applied to the opposing roll24. At this time, an electrostatic force from the intermediate transferbelt 20 toward the recording medium P acts on the pressure-responsiveparticle-applied section and the toner images, transferring thepressure-responsive particle-applied section and the toner images on theintermediate transfer belt 20 to the recording medium P.

The recording medium P to which the pressure-responsive particle-appliedsection and the toner images have been transferred is transported to athermal fixing device (an example of the thermal fixing unit) 28. Thethermal fixing device 28 includes a heat source, such as a halogenheater, and heats the recording medium P. The surface temperature of therecording medium P heated by the thermal fixing device 28 is preferably150° C. or higher and 220° C. or lower, more preferably 155° C. orhigher and 210° C. or lower, still more preferably 160° C. or higher and200° C. or lower. As the recording medium P passes through the thermalfixing device 28, the color toner images are thermally fixed to therecording medium P.

The thermal fixing device 28 may be a device that applies pressure underheating in order to prevent the pressure-responsive particles fromfalling off the recording medium P and improve the fixability of thecolor image to the recording medium P. The thermal fixing device 28 maybe, for example, a pair of fixing members (roll/roll, belt/roll) havinga heat source inside. When the thermal fixing device 28 appliespressure, the pressure applied to the recording medium P by the thermalfixing device 28 may be lower than the pressure applied to a recordingmedium P2 by a pressure device 230. Specifically, the pressure may be0.2 MPa or more and 1 MPa or less.

As the recording medium P passes through the printing unit 300, therecording medium P becomes a recording medium P1 having the color imageand the pressure-responsive particles thereon. The recording medium P1is transported toward the pressure-bonding unit 200.

The pressure-bonding unit 200 in FIG. 3 may have the same structure asthe pressure-bonding unit 200 in FIG. 2, and the structure and operationof the pressure-bonding unit 200 in FIG. 3 are not described in detail.

In the printed material producing apparatus according to the exemplaryembodiment, the printing unit 300 and the pressure-bonding unit 200 maybe adjacent to each other or may be distant from each other. When theprinting unit 300 and the pressure-bonding unit 200 are distant fromeach other, the printing unit 300 is connected to the pressure-bondingunit 200 through, for example, a transporting unit (e.g., a beltconveyor) that transports the recording medium P1.

The printed material producing apparatus according to the exemplaryembodiment may include a cutting unit that cuts a recording medium intoa predetermined size. Examples of the cutting unit include a cuttingunit that is disposed between the printing unit 300 and thepressure-bonding unit 200 and cuts away a region that is part of therecording medium P1 and that does not have the pressure-responsiveparticles thereon; a cutting unit that is disposed between the foldingdevice 220 and the pressure device 230 and cuts away a region that ispart of the recording medium P2 and that does not have thepressure-responsive particles thereon; and a cutting unit that isdisposed downstream of the pressure-bonding unit 200 and cuts away aregion that is part of the pressure-bonded printed material P3 and thatis not bonded with the pressure-responsive particles.

The printed material producing apparatus according to the exemplaryembodiment is not limited to a sheet-fed apparatus. The printed materialproducing apparatus according to the exemplary embodiment may be anapparatus that forms a long pressure-bonded printed material bysubjecting a long recording medium to the color image forming step, thedisposing step, and the pressure-bonding step, and then cuts the longpressure-bonded printed material into a predetermined size.

Process Cartridge

A process cartridge to be installed in a printed material producingapparatus using an electrophotographic system will be described.

A process cartridge according to an exemplary embodiment includes adeveloping unit that stores the electrostatic charge image developeraccording to the exemplary embodiment and that develops an electrostaticcharge image on the surface of a photoreceptor by using theelectrostatic charge image developer to form a pressure-responsiveparticle-applied section. The process cartridge is attachable to anddetachable from a printed material producing apparatus.

The process cartridge according to the exemplary embodiment may includea developing unit, and as necessary, at least one selected from aphotoreceptor, a charging unit, an electrostatic charge image formingunit, a transfer unit, and the like.

Exemplary embodiments of the process cartridge include a cartridgeincluding a photoreceptor and, on the periphery of the photoreceptor, acharging roll (an example of the charging unit), a developing device (anexample of the developing unit), and a photoreceptor cleaning device (anexample of the cleaning unit), which are integrated by a housing. Thehousing has an opening for exposure. The housing has an installationrail, and the process cartridge is attached to the printed materialproducing apparatus through the installation rail.

EXAMPLES

Exemplary embodiments of the present disclosure will be described belowin detail by way of Examples, but exemplary embodiments of the presentdisclosure are not limited to these Examples. In the followingdescription, the units “part” and “%” are on a mass basis, unlessotherwise specified.

Example 1 Preparation of Styrene-Based Resin Particle Dispersion St1

Styrene (St): 370 parts

n-Butyl acrylate (BA): 115 parts

Acrylic acid (AA): 15 parts

Dodecanethiol: 7.5 parts

The above materials are mixed and dissolved to prepare a monomersolution.

An anionic surfactant (DOWFAX 2A1 available from The Dow ChemicalCompany) (8 parts) is dissolved in 205 parts of ion exchange water, andthe monomer solution is added to the resulting solution and dispersed toform an emulsion.

The anionic surfactant (2.2 parts) is dissolved in 462 parts of ionexchange water, and the resulting solution is placed in a flask forpolymerization equipped with a stirrer, a thermometer, a refluxcondenser, and a nitrogen gas inlet tube. The solution is heated to 73°C. under stirring and held at this temperature.

Ammonium persulfate (3 parts) is dissolved in 21 parts of ion exchangewater, and the resulting solution is added dropwise to the flask forpolymerization through a metering pump over 15 minutes, and the emulsionis then added dropwise over 160 minutes through a metering pump.

Next, the flask for polymerization is held at 75° C. for three hoursunder gentle stirring, and then returned to room temperature (25° C.,the same applies hereinafter).

This process produces a styrene-based resin particle dispersion St1having a volume average particle size (D50v) of 220 nm, a weight averagemolecular weight of 33,000 as determined by GPC (UV detection), a glasstransition temperature of 53° C., and a solid content of 42%.

Preparation of Composite Resin Particle Dispersion SM1

Styrene-based resin particle dispersion St1: 400 parts (solid content)

2-Ethylhexyl acrylate (2EHA): 250 parts

n-Butyl acrylate (BA): 150 parts

Ion exchange water: 982 parts

The above materials are placed in a flask for polymerization, stirred at25° C. for one hour, and then heated to 70° C. Ammonium persulfate (2.5parts) is dissolved in 75 parts of ion exchange water, and the resultingsolution is added dropwise to the flask for polymerization through ametering pump over 60 minutes. Next, the flask for polymerization isheld at 70° C. for three hours under gentle stirring, and then returnedto room temperature.

This process produces a composite resin particle dispersion SM1 that hasa solid content of 32% and in which the composite resin particles have avolume average particle size (D50v) of 219 nm, and the resin of thecomposite resin particles has a weight average molecular weight of220,000 as determined by GPC (UV detection).

Preparation of Pressure-Responsive Particles

Composite resin particle dispersion SM1: 180 parts (solid content)

Anionic surfactant: 1 part

These components are placed in a reactor and mixed. While the mixture isdispersed with a homogenizer (5,000 rpm), 1.2 parts of 17% aluminumsulfate is added and dispersed for 6 minutes. The resulting dispersionis then heated to grow aggregation and cooled to 49° C. from the timepoint at which the particle size reaches 10 μm (liquid temperature: 57°C.). Subsequently, 40 parts (solid content) of the styrene-based resinparticle dispersion St1 and 1.3 parts of polyaluminum chloride areadded, and the dispersion mixture is heated to 55° C. and maintained at55° C. for 30 minutes. The dispersion is then heated to 90° C. to causecoalescence, followed by filtration, washing, and drying. This processproduces pressure-responsive particles (EA1) having a volume averageparticle size of 10.5 μm and an average circularity of 0.967.

Examples 2 to 5 Preparation of Composite Resin Particle Dispersions SM2to SM5

Composite resin particle dispersions SM2 to SM5 are prepared in the samemanner as in the preparation of the composite resin particle dispersionSM1 except that the acrylic acid monomers are changed to thecompositions shown in Table 1.

Pressure-responsive particles (EA2 to EA5) are prepared in the samemanner as that in Example 1 except that the composite resin particledispersions SM2 to SM5 are used instead of the composite resin particledispersion SM1.

Examples 6 to 9 Preparation of Styrene-Based Resin Particle DispersionsSt2 to St5

Styrene-based resin particle dispersions St2 to St5 are prepared in thesame manner as that for the styrene-based resin particle dispersion St1except that the styrenic monomers are changed to the compositions shownin Table 1.

Preparation of Composite Resin Particle Dispersions SM6 to SM9

Composite resin particle dispersions SM6 to SM9 are prepared in the samemanner as that for the composite resin particle dispersion SM1 exceptthat the styrene-based resin particle dispersions St2 to St5 are usedinstead of the styrene-based resin particle dispersion St1.

Pressure-responsive particles (EA6 to EA9) are produced in the samemanner as that in Example 1 except that the composite resin particledispersions SM6 to SM9 are used instead of the composite resin particledispersion SM1.

Examples 10 and 11 Preparation of Composite Resin Particle DispersionsSM10 and SM11

Composite resin particle dispersions SM10 to SM11 are prepared in thesame manner as that for the composite resin particle dispersion SM1except that the amounts of acrylic monomers are changed such that themass ratio of the (meth)acrylic acid ester-based resin (Ac) to thestyrene-based resin (St) is as shown in Table 1.

Pressure-responsive particles (EA10 and EA11) are produced in the samemanner as that in Example 1 except that the composite resin particledispersions SM10 and SM11 are used instead of the composite resinparticle dispersion SM1.

Example 12

Pressure-responsive particles (EA12) are produced in the same manner asthat in Example 1 except that, in the shell forming step, the amount ofthe styrene-based resin particle dispersion St1 is changed to 11.5 parts(solid content), and the amount of polyaluminum chloride added is alsochanged to the amount of aggregating agent added as described in Table1.

Example 13

Pressure-responsive particles (EA13) are produced in the same manner asthat in Example 1 except that, in the shell forming step, the amount ofthe styrene-based resin particle dispersion St1 is changed to 110 parts(solid content), and the amount of polyaluminum chloride added is alsochanged to the amount of aggregating agent added as described in Table1.

Example 14

Pressure-responsive particles (EA14) are produced in the same manner asthat in Example 1 except that, in the shell forming step, 0.77 parts ofaluminum sulfate is added instead of polyaluminum chloride.

Example 15

Pressure-responsive particles (EA15) are produced in the same manner asthat in Example 1 except that, in the shell forming step, thestyrene-based resin particle dispersion is added without cooling theliquid.

Example 16

Pressure-responsive particles (EA16) are produced in the same manner asthat in Example 1 except that, in preparing the pressure-responsiveparticles, 13.2 parts (solid content) of a silica dispersion (solidcontent: 21 mass %, particle size 12 nm) is added together with thecomposite resin particle dispersion SM1 and an anionic surfactant.

Example 17

Pressure-responsive particles (EA17) are produced in the same manner asthat in Example 2 except that, in preparing the pressure-responsiveresin particles, 4.4 parts (solid content) of a silica dispersion (solidcontent: 21 mass %, particle size 7 nm) is added together with thecomposite resin particle dispersion SM1 and an anionic surfactant.

Example 18

Pressure-responsive particles (EA18) are produced in the same manner asthat in Example 3 except that, in preparing the pressure-responsiveresin particles, 17.6 parts (solid content) of a silica dispersion(solid content: 21 mass %, particle size 40 nm) is added together withthe composite resin particle dispersion SM1 and an anionic surfactant.

Comparative Example 1

Pressure-responsive resin particles (EA19) are produced in the samemanner as that in Example 1 except that the amount of polyaluminumchloride added is changed from 1.3 parts to 0.04 parts.

Comparative Example 2

Pressure-responsive resin particles (EA20) are produced in the samemanner as that in Example 1 except that the amount of polyaluminumchloride added is changed to the value described in Table 1.

Comparative Examples 3 and 4

Pressure-responsive resin particles (EA21 and EA22) are produced in thesame manner as in Example 1 except that the ratio between the amount ofthe styrene-based resin particle dispersion St1 used and the amount of2-ethylhexyl acrylate and n-butyl acrylate monomers used to prepare thecomposite resin particle dispersion SM1 is changed to the valuesdescribed in Table 1.

Evaluation of Tackiness

To a sheet of paper on which a text image has been printed with anelectrophotographic printer, the pressure-responsive particles areuniformly applied with a cake printer at two standards of 2.0 g/m² and1.5 g/m² at a voltage of 100 V by sprinkling the pressure-responsiveresin particles on a mesh with a mesh size of 50 μm. Thepressure-responsive particles are fixed to the sheet of paper by using afixing bench of a multifunction printer. The sheet of paper is folded intwo so that the image is on the inside, and then pressed (Gap 10)through a sealer (Pressle multi2 available from Toppan Forms Co., Ltd.).The pressed sheet of paper is left to stand overnight and then cut intoa width of 15 mm, which is then subjected to a 90-degree peel test tomeasure the peel force (unit: N/15 mm) and evaluate tackiness.

The evaluation criteria are described below.

S: ≥0.8 N/15 mm for 1.5 g/m² sample

A: ≥0.8 N/15 mm for 2.0 g/m² sample

B: more than 0.4 N/15 mm and less than 0.8 N/15 mm for 2.0 g/m² sample

C: ≤0.4 N/15 mm for 2.0 g/m² sample

Grade S, A, or B is preferred, Grade S or A is more preferred, and GradeS is still more preferred.

Evaluation of Dispersion Storage Stability

In preparing the pressure-responsive particles, the pressure-responsiveparticle dispersion after heating to 90° C. to cause coalescence butbefore filtration is cooled to 30° C. and then stored in a sealedchamber at 30° C. for one month. The particle size distribution is thenmeasured by Coulter LS. If aggregated particles are formed, the measuredvolume average particle size distribution has two peaks with one peak onthe coarse particle side. The evaluation criteria are described below.

A: The volume average particle size distribution has one peak, which isthe same particle size distribution as the initial one.

B: The volume average particle size distribution has two peaks with onepeak on the coarse particle side and returns to one peak afterre-stirring.

C: The volume average particle size distribution has two peaks with onepeak on the coarse particle side and does not return to one peak evenafter re-stirring.

Grade A or B is preferred, and Grade A is more preferred.

Adhesion of Aggregates and Fusion-Bonded Materials

The adhesion of aggregates and fused materials is evaluated on the basisof the following evaluation criteria according to the applicationconditions and mesh conditions after the pressure-responsive particlesare applied to 200 sheets of paper with the cake printer in thetackiness evaluation.

A: The pressure-responsive particles can be continuously applied withoutany problem.

B: There is some clogging of the mesh, but the pressure-responsiveparticles can be applied after the mesh is blown during application.

C: The mesh is clogged with the pressure-responsive particles, and thepressure-responsive particles cannot be applied even after the mesh isblown.

The evaluation results are summarized in Table 1.

TABLE 1 Shell Forming Step Amount of Amount of Styrene-Based SilicaAdded Resin Particles (Meth)Acrylic Acid Relative to Added RelativeStyrene-Based Resin Ester-Based Resin Total Mass to Total Mass ResinMass Ratio of Mass Ratio of of Composite of Composite Particle PolymerTg Polymer Tg Resin Particles Resin Particles Dispersion Components (°C.) Components (° C.) (mass %) (mass %) Example 1 St1 St/BA/AA = 532EHA/BA = −50 — 18 74/23/3 62/38 Example 2 St1 St/BA/AA = 53 2EHA/PA =−46 — 18 74/23/3 38/62 Example 3 St1 St/BA/AA = 53 2EHA/HA = −52 — 1874/23/3 38/62 Example 4 St1 St/BA/AA = 53 2EHA/BA = −55 — 18 74/23/325/75 Example 5 St1 St/BA/AA = 53 2EHA/BA = −50 — 18 74/23/3 75/25Example 6 St2 St/2EHA/AA = 55 2EHA/BA = −50 — 18 74/23/3 62/38 Example 1St3 St/EA/AA = 55 2EHA/BA = −50 — 18 64/33/3 62/38 Example 8 St4St/BA/AA = 56 2EHA/BA = −50 — 18 85/10/5 62/38 Example 9 St5 St/BA/AA =53 2EHA/BA = −50 — 18 74/23/3 62/38 Example 10 St1 St/BA/AA = 53 2EHA/BA= −50 — 18 74/23/3 62/38 Example 11 St1 St/BA/AA = 53 2EHA/BA = −50 — 1874/23/3 62/38 Example 12 St1 St/BA/AA = 53 2EHA/BA = −50 — 6 74/23/362/38 Example 13 St1 St/BA/AA = 53 2EHA/BA = −50 — 38 74/23/3 62/38Example 14 St1 St/BA/AA = 53 2EHA/BA = −50 — 18 74/23/3 62/38 Example 15St1 St/BA/AA = 53 2EHA/BA = −50 — 18 74/23/3 62/38 Example 16 St1St/BA/AA = 53 2EHA/BA = −50 6% (12 nm silica) 18 74/23/3 62/38 Example17 St1 St/BA/AA = 53 2EHA/PA = −46 2% (7 nm silica)  18 74/23/3 38/62Example 18 St1 St/BA/AA = 53 2EHA/HA = −52 8% (40 nm silica) 18 74/23/338/62 Comparative St1 St/BA/AA = 53 2EHA/BA = −50 — 18 Example 1 74/23/362/38 Comparative St1 St/BA/AA = 53 2EHA/BA = −50 — 18 Example 2 74/23/362/38 Comparative St1 St/BA/AA = 53 2EHA/BA = −50 — 18 Example 3 74/23/362/38 Comparative St1 St/BA/AA = 53 2EHA/BA = −50 — 18 Example 4 74/23/362/38 Shell Forming Step Pressure- Amount of Responsive AggregatingParticles Agent Added Mass Ratio of Relative to (Meth)Acrylic Presenceof Total Mass Acid Ester-Based Aggregates Type of of Composite Resin(Ac) to Dispersion and Fusion- Aggregating Resin Particles Styrene-BasedStorage Bonded Agent (mass %) Resin (St) Tackiness Stability MaterialsExample 1 polyaluminum 0.59 Ac/St = 41/59 A A A chloride Example 2polyaluminum 0.59 Ac/St = 41/59 A A A chloride Example 3 polyaluminum0.59 Ac/St = 41/59 A A A chloride Example 4 polyaluminum 0.59 Ac/St =41/59 A A A chloride Example 5 polyaluminum 0.59 Ac/St = 41/59 A A Achloride Example 6 polyaluminum 0.59 Ac/St = 41/59 A A A chlorideExample 1 polyaluminum 0.59 Ac/St = 41/59 A A A chloride Example 8polyaluminum 0.59 Ac/St = 41/59 A A A chloride Example 9 polyaluminum0.59 Ac/St = 41/59 A A A chloride Example 10 polyaluminum 0.59 Ac/St =77/23 A B A chloride Example 11 polyaluminum 0.59 Ac/St = 24/76 B A Achloride Example 12 polyaluminum 0.11 Ac/St = 47/53 A B B chlorideExample 13 polyaluminum 0.98 Ac/St = 31/69 B A A chloride Example 14aluminum 0.35 Ac/St = 41/59 A A B sulfate Example 15 polyaluminum 0.59Ac/St = 41/59 A A B chloride Example 16 polyaluminum 0.59 Ac/St = 41/59S A A chloride Example 17 polyaluminum 0.59 Ac/St = 41/59 S A A chlorideExample 18 polyaluminum 0.59 Ac/St = 41/59 S A A chloride Comparativepolyaluminum 0.09 Ac/St = 41/59 A C C Example 1 chloride Comparativepolyaluminum 1.01 Ac/St = 41/59 C A A Example 2 chloride Comparativepolyaluminum 0.59 Ac/St = 83/17 A C C Example 3 chloride Comparativepolyaluminum 0.59 Ac/St = 16/84 C A A Example 4 chloride

The above results indicate that Examples show better tackiness at thetime of pressure bonding and better dispersion storage stability andgenerate less aggregates and fusion-bonded materials than ComparativeExamples.

The foregoing description of the exemplary embodiments of the presentdisclosure has been provided for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit thedisclosure to the precise forms disclosed. Obviously, many modificationsand variations will be apparent to practitioners skilled in the art. Theembodiments were chosen and described in order to best explain theprinciples of the disclosure and its practical applications, therebyenabling others skilled in the art to understand the disclosure forvarious embodiments and with the various modifications as are suited tothe particular use contemplated. It is intended that the scope of thedisclosure be defined by the following claims and their equivalents.

What is claimed is:
 1. A method for producing pressure-responsiveparticles, the method comprising: adding an aggregating agent to adispersion containing composite resin particles containing astyrene-based resin including a styrene compound and a vinyl monomerother than the styrene compound as polymer components and a(meth)acrylic acid ester-based resin including a (meth)acrylic acidester compound as a polymer component to aggregate the composite resinparticles so as to form aggregated particles A; forming a shell byadding an aggregating agent and styrene-based resin particles containinga styrene compound and a vinyl monomer other than the styrene compoundas polymer components to a dispersion containing the aggregatedparticles A to aggregate the styrene-based resin particles so as to formaggregated particles B; and heating and fusing the aggregated particlesB to form pressure-responsive particles, wherein an amount of thestyrene-based resin particles added in the formation of the shell is 5mass % or more and 40 mass % or less relative to a total mass of thecomposite resin particles, an amount of the aggregating agent added inthe formation of the shell is 0.1 mass % or more and 1.0 mass % or lessrelative to the total mass of the composite resin particles, a massratio of the styrene-based resin to the (meth)acrylic acid ester-basedresin in the pressure-responsive particles is from 80:20 to 20:80, and adifference between the lowest glass transition temperature and thehighest glass transition temperature of resins contained in thepressure-responsive particles is 30° C. or more.
 2. The method forproducing pressure-responsive particles according to claim 1, wherein,in the formation of the shell, the aggregating agent and thestyrene-based resin particles containing a styrene compound and a vinylmonomer other than the styrene compound as polymer components are addedafter a liquid temperature of the dispersion containing the aggregatedparticles A is lowered after the aggregation of the composite resinparticles.
 3. The method for producing pressure-responsive particlesaccording to claim 2, wherein, in the formation of the shell, the liquidtemperature of the dispersion is lowered by 5° C. or more before thestyrene-based resin particles and the aggregating agent are added. 4.The method for producing pressure-responsive particles according toclaim 1, wherein the aggregating agent in the aggregation of thecomposite resin particles and the aggregating agent in the formation ofthe shell are aluminum-containing aggregating agents.
 5. The method forproducing pressure-responsive particles according to claim 4, whereinthe aggregating agent in the aggregation of the composite resinparticles is aluminum sulfate.
 6. The method for producingpressure-responsive particles according to claim 1, wherein silicaparticles are added in the aggregation of the composite resin particles.7. The method for producing pressure-responsive particles according toclaim 6, wherein an amount of the silica particles added in theaggregation of the composite resin particles is 2 mass % or more and 8mass % or less relative to the total mass of the pressure-responsiveparticles.
 8. The method for producing pressure-responsive particlesaccording to claim 6, wherein the silica particles have an arithmeticmean particle size of 7 nm or more and 40 nm or less.
 9. The method forproducing pressure-responsive particles according to claim 1, whereinthe styrene-based resin contained in the pressure-responsive particleshas a glass transition temperature of 30° C. or higher.
 10. The methodfor producing pressure-responsive particles according to claim 1,wherein the (meth)acrylic acid ester-based resin contained in thepressure-responsive particles has a glass transition temperature of −30°C. or lower.
 11. A method for producing a printed material, the methodcomprising: disposing, on a recording medium, pressure-responsiveparticles produced by the method for producing pressure-responsiveparticles according to claim 1; and folding the recording medium andpressure-bonding the folded recording medium, or stacking the recordingmedium and another recording medium on top of each other andpressure-bonding the stacked recording media to each other.
 12. A methodfor producing a sheet for producing a printed material, the methodcomprising: disposing, on a substrate, pressure-responsive particlesproduced by the method for producing pressure-responsive particlesaccording to claim
 1. 13. Pressure-responsive particles produced by themethod for producing pressure-responsive particles according to claim 1.